We have been exploring several commands that allow us to use the OS via the CLI.
But some questions arise, basically search things seems a difficult task, but there are some very useful commands that help us to do these kind of things.
grep¶The procipal use of grep is to search a specific text (string) on a particular set of files.
This is one of the most used programs on the shell,
grep "String to Search" group_of_files
And we'll get on the standard output the lines of the files which contain the specific string we are searching for.
Try out the first part of the Homework.
cat file1.txt
THIS LINE IS AN UPPER CASE LINE IN THIS FILE. ESTA ES UNA LÍNEA EN MAYÚSCULAS. this line is the a lower case line in this file. esta es una línea en minúsculas. This Line Has All Its First Character Of The Word With Upper Case. Esta Línea Tiene La Primera Letra De Cada Palabra En Mayúsulas. And this is the last line. Esta es la última línea.
grep 'es' file1.txt
esta es una línea en minúsculas. Esta es la última línea.
But, there are times, where we are not interested if we have or not, uppercase (lowercase) characters, so we can use the insensitive case
grep -i 'es' file1.txt
ESTA ES UNA LÍNEA EN MAYÚSCULAS. esta es una línea en minúsculas. Esta Línea Tiene La Primera Letra De Cada Palabra En Mayúsulas. Esta es la última línea.
There is no difference if we use ' or "
grep -i "es" file1.txt
ESTA ES UNA LÍNEA EN MAYÚSCULAS. esta es una línea en minúsculas. Esta Línea Tiene La Primera Letra De Cada Palabra En Mayúsulas. Esta es la última línea.
Some times we want to have exactly the word we are looking for, not the string to be part of a different word,
grep -iw "es" file1.txt
ESTA ES UNA LÍNEA EN MAYÚSCULAS. esta es una línea en minúsculas. Esta es la última línea.
Let see the manual!
man grep
GREP(1) BSD General Commands Manual GREP(1)
NAME
grep, egrep, fgrep, zgrep, zegrep, zfgrep -- file pattern searcher
SYNOPSIS
grep [-abcdDEFGHhIiJLlmnOopqRSsUVvwxZ] [-A num] [-B num] [-C[num]]
[-e pattern] [-f file] [--binary-files=value] [--color[=when]]
[--colour[=when]] [--context[=num]] [--label] [--line-buffered]
[--null] [pattern] [file ...]
DESCRIPTION
The grep utility searches any given input files, selecting lines that
match one or more patterns. By default, a pattern matches an input line
if the regular expression (RE) in the pattern matches the input line
without its trailing newline. An empty expression matches every line.
Each input line that matches at least one of the patterns is written to
the standard output.
grep is used for simple patterns and basic regular expressions (BREs);
egrep can handle extended regular expressions (EREs). See re_format(7)
for more information on regular expressions. fgrep is quicker than both
grep and egrep, but can only handle fixed patterns (i.e. it does not
interpret regular expressions). Patterns may consist of one or more
lines, allowing any of the pattern lines to match a portion of the input.
zgrep, zegrep, and zfgrep act like grep, egrep, and fgrep, respectively,
but accept input files compressed with the compress(1) or gzip(1) com-
pression utilities.
The following options are available:
-A num, --after-context=num
Print num lines of trailing context after each match. See also
the -B and -C options.
-a, --text
Treat all files as ASCII text. Normally grep will simply print
``Binary file ... matches'' if files contain binary characters.
Use of this option forces grep to output lines matching the spec-
ified pattern.
-B num, --before-context=num
Print num lines of leading context before each match. See also
the -A and -C options.
-b, --byte-offset
The offset in bytes of a matched pattern is displayed in front of
the respective matched line.
-C[num, --context=num]
Print num lines of leading and trailing context surrounding each
match. The default is 2 and is equivalent to -A 2 -B 2. Note:
no whitespace may be given between the option and its argument.
-c, --count
Only a count of selected lines is written to standard output.
--colour=[when, --color=[when]]
Mark up the matching text with the expression stored in
GREP_COLOR environment variable. The possible values of when can
be `never', `always' or `auto'.
-D action, --devices=action
Specify the demanded action for devices, FIFOs and sockets. The
default action is `read', which means, that they are read as if
they were normal files. If the action is set to `skip', devices
will be silently skipped.
-d action, --directories=action
Specify the demanded action for directories. It is `read' by
default, which means that the directories are read in the same
manner as normal files. Other possible values are `skip' to
silently ignore the directories, and `recurse' to read them
recursively, which has the same effect as the -R and -r option.
-E, --extended-regexp
Interpret pattern as an extended regular expression (i.e. force
grep to behave as egrep).
-e pattern, --regexp=pattern
Specify a pattern used during the search of the input: an input
line is selected if it matches any of the specified patterns.
This option is most useful when multiple -e options are used to
specify multiple patterns, or when a pattern begins with a dash
(`-').
--exclude
If specified, it excludes files matching the given filename pat-
tern from the search. Note that --exclude patterns take priority
over --include patterns, and if no --include pattern is speci-
fied, all files are searched that are not excluded. Patterns are
matched to the full path specified, not only to the filename com-
ponent.
--exclude-dir
If -R is specified, it excludes directories matching the given
filename pattern from the search. Note that --exclude-dir pat-
terns take priority over --include-dir patterns, and if no
--include-dir pattern is specified, all directories are searched
that are not excluded.
-F, --fixed-strings
Interpret pattern as a set of fixed strings (i.e. force grep to
behave as fgrep).
-f file, --file=file
Read one or more newline separated patterns from file. Empty
pattern lines match every input line. Newlines are not consid-
ered part of a pattern. If file is empty, nothing is matched.
-G, --basic-regexp
Interpret pattern as a basic regular expression (i.e. force grep
to behave as traditional grep).
-H Always print filename headers with output lines.
-h, --no-filename
Never print filename headers (i.e. filenames) with output lines.
--help Print a brief help message.
-I Ignore binary files. This option is equivalent to
--binary-file=without-match option.
-i, --ignore-case
Perform case insensitive matching. By default, grep is case sen-
sitive.
--include
If specified, only files matching the given filename pattern are
searched. Note that --exclude patterns take priority over
--include patterns. Patterns are matched to the full path speci-
fied, not only to the filename component.
--include-dir
If -R is specified, only directories matching the given filename
pattern are searched. Note that --exclude-dir patterns take pri-
ority over --include-dir patterns.
-J, --bz2decompress
Decompress the bzip2(1) compressed file before looking for the
text.
-L, --files-without-match
Only the names of files not containing selected lines are written
to standard output. Pathnames are listed once per file searched.
If the standard input is searched, the string ``(standard
input)'' is written.
-l, --files-with-matches
Only the names of files containing selected lines are written to
standard output. grep will only search a file until a match has
been found, making searches potentially less expensive. Path-
names are listed once per file searched. If the standard input
is searched, the string ``(standard input)'' is written.
--mmap Use mmap(2) instead of read(2) to read input, which can result in
better performance under some circumstances but can cause unde-
fined behaviour.
-m num, --max-count=num
Stop reading the file after num matches.
-n, --line-number
Each output line is preceded by its relative line number in the
file, starting at line 1. The line number counter is reset for
each file processed. This option is ignored if -c, -L, -l, or -q
is specified.
--null Prints a zero-byte after the file name.
-O If -R is specified, follow symbolic links only if they were
explicitly listed on the command line. The default is not to
follow symbolic links.
-o, --only-matching
Prints only the matching part of the lines.
-p If -R is specified, no symbolic links are followed. This is the
default.
-q, --quiet, --silent
Quiet mode: suppress normal output. grep will only search a file
until a match has been found, making searches potentially less
expensive.
-R, -r, --recursive
Recursively search subdirectories listed.
-S If -R is specified, all symbolic links are followed. The default
is not to follow symbolic links.
-s, --no-messages
Silent mode. Nonexistent and unreadable files are ignored (i.e.
their error messages are suppressed).
-U, --binary
Search binary files, but do not attempt to print them.
-V, --version
Display version information and exit.
-v, --invert-match
Selected lines are those not matching any of the specified pat-
terns.
-w, --word-regexp
The expression is searched for as a word (as if surrounded by
`[[:<:]]' and `[[:>:]]'; see re_format(7)).
-x, --line-regexp
Only input lines selected against an entire fixed string or regu-
lar expression are considered to be matching lines.
-y Equivalent to -i. Obsoleted.
-Z, -z, --decompress
Force grep to behave as zgrep.
--binary-files=value
Controls searching and printing of binary files. Options are
binary, the default: search binary files but do not print them;
without-match: do not search binary files; and text: treat all
files as text.
--context[=num]
Print num lines of leading and trailing context. The default is
2.
--line-buffered
Force output to be line buffered. By default, output is line
buffered when standard output is a terminal and block buffered
otherwise.
If no file arguments are specified, the standard input is used.
ENVIRONMENT
GREP_OPTIONS May be used to specify default options that will be placed
at the beginning of the argument list. Backslash-escaping
is not supported, unlike the behavior in GNU grep.
EXIT STATUS
The grep utility exits with one of the following values:
0 One or more lines were selected.
1 No lines were selected.
>1 An error occurred.
EXAMPLES
To find all occurrences of the word `patricia' in a file:
$ grep 'patricia' myfile
To find all occurrences of the pattern `.Pp' at the beginning of a line:
$ grep '^\.Pp' myfile
The apostrophes ensure the entire expression is evaluated by grep instead
of by the user's shell. The caret `^' matches the null string at the
beginning of a line, and the `\' escapes the `.', which would otherwise
match any character.
To find all lines in a file which do not contain the words `foo' or
`bar':
$ grep -v -e 'foo' -e 'bar' myfile
A simple example of an extended regular expression:
$ egrep '19|20|25' calendar
Peruses the file `calendar' looking for either 19, 20, or 25.
SEE ALSO
ed(1), ex(1), gzip(1), sed(1), re_format(7)
STANDARDS
The grep utility is compliant with the IEEE Std 1003.1-2008 (``POSIX.1'')
specification.
The flags [-AaBbCDdGHhIJLmoPRSUVwZ] are extensions to that specification,
and the behaviour of the -f flag when used with an empty pattern file is
left undefined.
All long options are provided for compatibility with GNU versions of this
utility.
Historic versions of the grep utility also supported the flags [-ruy].
This implementation supports those options; however, their use is
strongly discouraged.
HISTORY
The grep command first appeared in Version 6 AT&T UNIX.
BUGS
The grep utility does not normalize Unicode input, so a pattern contain-
ing composed characters will not match decomposed input, and vice versa.
BSD July 28, 2010 BSD
From Aho, Weinberger and Kernighan, the names of its authors.
Very good when managing data on the terminal.
Generally, the syntax goes as follows
awk '/pattern1/ {What to do}
/pattern2/ {What to do}' Group_of_files
cat file1.txt
THIS LINE IS AN UPPER CASE LINE IN THIS FILE. ESTA ES UNA LÍNEA EN MAYÚSCULAS. this line is the a lower case line in this file. esta es una línea en minúsculas. This Line Has All Its First Character Of The Word With Upper Case. Esta Línea Tiene La Primera Letra De Cada Palabra En Mayúsulas. And this is the last line. Esta es la última línea.
To print a complete file usinng awk, we use the instruction print
awk '{print;}' file1.txt
THIS LINE IS AN UPPER CASE LINE IN THIS FILE. ESTA ES UNA LÍNEA EN MAYÚSCULAS. this line is the a lower case line in this file. esta es una línea en minúsculas. This Line Has All Its First Character Of The Word With Upper Case. Esta Línea Tiene La Primera Letra De Cada Palabra En Mayúsulas. And this is the last line. Esta es la última línea.
The patterns we are using can be used to search similarly as grep
awk '/This/' file1.txt
This Line Has All Its First Character Of The Word With Upper Case.
Is usual, in different programming languages that $ means a column, or a numeration that is implicit, so it is the case.
awk '{print $2;}' file1.txt
LINE ES line es Line Línea this es
And can be combined!
awk '{print $5,$2;}' file1.txt
UPPER LINE EN ES a line en es Its Line Primera Línea last this línea. es
There are also some variables already defined,
awk '{print $5,$2,$NF;}' file1.txt
UPPER LINE FILE. EN ES MAYÚSCULAS. a line file. en es minúsculas. Its Line Case. Primera Línea Mayúsulas. last this line. línea. es línea.
Let's use our own data,
awk '{print;}' DataHw1a.dat
1 jf.escobarr José 17 Geociencias 2 asesquivel Andrea 18 Fisica 3 df.rodriguezg Diego 20 Fisica 4 l.garciae Laura 18 Geociencias 5 aj.mendoza Alberto 19 geociencias 6 ke.solano Kevin 17 Geociencias 7 sm.morelli Sebastian 18 Física 8 bj.anaya Bryan 19 Física 9 sm.gutierrez Sharol 19 Física 10 am.forero1 ana 20 Ingenieria Electronica y Geociencias 11 ac.melo Angie 17 Física 12 b.taborda Brayan 18 Física 13 df.vegao Daniel 18 Geociencias 14 lp.cardozo Lina 18 Ingeniería de Sistema 15 s.pastrana Santiago 21 Ingeniería Industrial 16 v.castilloc Valeria 19 Fisica 17 f_ariasc Fabio 18 Física 18 e.cayon Edgardo 20 Fisica 19 sp.joven Susan 19 Ingeniería de Sistemas 20 e.gonzalezr Emilio 20 Ingeniería de Sistemas 21 s.posadac Sofia 18 Ingeniería Mecánica 22 js.velasco Juan 18 Ingenieria Ambietal y Geocienicas 23 j.sevillam Mauricio 80 Prof
Data can be filtred!!
awk '$4<19' DataHw1a.dat
1 jf.escobarr José 17 Geociencias 2 asesquivel Andrea 18 Fisica 4 l.garciae Laura 18 Geociencias 6 ke.solano Kevin 17 Geociencias 7 sm.morelli Sebastian 18 Física 11 ac.melo Angie 17 Física 12 b.taborda Brayan 18 Física 13 df.vegao Daniel 18 Geociencias 14 lp.cardozo Lina 18 Ingeniería de Sistema 17 f_ariasc Fabio 18 Física 21 s.posadac Sofia 18 Ingeniería Mecánica 22 js.velasco Juan 18 Ingenieria Ambietal y Geocienicas
awk '$5 ~ /Ingeniería/' DataHw1a.dat
14 lp.cardozo Lina 18 Ingeniería de Sistema 15 s.pastrana Santiago 21 Ingeniería Industrial 19 sp.joven Susan 19 Ingeniería de Sistemas 20 e.gonzalezr Emilio 20 Ingeniería de Sistemas 21 s.posadac Sofia 18 Ingeniería Mecánica
Let us explore the manual,
man awk
AWK(1) AWK(1)
awk
NAME
awk - pattern-directed scanning and processing language
SYNOPSIS
awk [ -F fs ] [ -v var=value ] [ 'prog' | -f progfile ] [ file ... ]
DESCRIPTION
Awk scans each input file for lines that match any of a set of patterns
specified literally in prog or in one or more files specified as -f
progfile. With each pattern there can be an associated action that
will be performed when a line of a file matches the pattern. Each line
is matched against the pattern portion of every pattern-action state-
ment; the associated action is performed for each matched pattern. The
file name - means the standard input. Any file of the form var=value
is treated as an assignment, not a filename, and is executed at the
time it would have been opened if it were a filename. The option -v
followed by var=value is an assignment to be done before prog is exe-
cuted; any number of -v options may be present. The -F fs option
defines the input field separator to be the regular expression fs.
An input line is normally made up of fields separated by white space,
or by regular expression FS. The fields are denoted $1, $2, ..., while
$0 refers to the entire line. If FS is null, the input line is split
into one field per character.
A pattern-action statement has the form
pattern { action }
A missing { action } means print the line; a missing pattern always
matches. Pattern-action statements are separated by newlines or semi-
colons.
An action is a sequence of statements. A statement can be one of the
following:
if( expression ) statement [ else statement ]
while( expression ) statement
for( expression ; expression ; expression ) statement
for( var in array ) statement
do statement while( expression )
break
continue
{ [ statement ... ] }
expression # commonly var = expression
print [ expression-list ] [ > expression ]
printf format [ , expression-list ] [ > expression ]
return [ expression ]
next # skip remaining patterns on this input line
nextfile # skip rest of this file, open next, start at top
delete array[ expression ]# delete an array element
delete array # delete all elements of array
exit [ expression ] # exit immediately; status is expression
Statements are terminated by semicolons, newlines or right braces. An
empty expression-list stands for $0. String constants are quoted " ",
with the usual C escapes recognized within. Expressions take on string
or numeric values as appropriate, and are built using the operators + -
* / % ^ (exponentiation), and concatenation (indicated by white space).
The operators ! ++ -- += -= *= /= %= ^= > >= < <= == != ?: are also
available in expressions. Variables may be scalars, array elements
(denoted x[i]) or fields. Variables are initialized to the null
string. Array subscripts may be any string, not necessarily numeric;
this allows for a form of associative memory. Multiple subscripts such
as [i,j,k] are permitted; the constituents are concatenated, separated
by the value of SUBSEP.
The print statement prints its arguments on the standard output (or on
a file if >file or >>file is present or on a pipe if |cmd is present),
separated by the current output field separator, and terminated by the
output record separator. file and cmd may be literal names or paren-
thesized expressions; identical string values in different statements
denote the same open file. The printf statement formats its expression
list according to the format (see printf(3)). The built-in function
close(expr) closes the file or pipe expr. The built-in function
fflush(expr) flushes any buffered output for the file or pipe expr.
The mathematical functions exp, log, sqrt, sin, cos, and atan2 are
built in. Other built-in functions:
length the length of its argument taken as a string, or of $0 if no
argument.
rand random number on (0,1)
srand sets seed for rand and returns the previous seed.
int truncates to an integer value
substr(s, m, n)
the n-character substring of s that begins at position m counted
from 1.
index(s, t)
the position in s where the string t occurs, or 0 if it does
not.
match(s, r)
the position in s where the regular expression r occurs, or 0 if
it does not. The variables RSTART and RLENGTH are set to the
position and length of the matched string.
split(s, a, fs)
splits the string s into array elements a[1], a[2], ..., a[n],
and returns n. The separation is done with the regular expres-
sion fs or with the field separator FS if fs is not given. An
empty string as field separator splits the string into one array
element per character.
sub(r, t, s)
substitutes t for the first occurrence of the regular expression
r in the string s. If s is not given, $0 is used.
gsub same as sub except that all occurrences of the regular expres-
sion are replaced; sub and gsub return the number of replace-
ments.
sprintf(fmt, expr, ... )
the string resulting from formatting expr ... according to the
printf(3) format fmt
system(cmd)
executes cmd and returns its exit status
tolower(str)
returns a copy of str with all upper-case characters translated
to their corresponding lower-case equivalents.
toupper(str)
returns a copy of str with all lower-case characters translated
to their corresponding upper-case equivalents.
The ``function'' getline sets $0 to the next input record from the cur-
rent input file; getline <file sets $0 to the next record from file.
getline x sets variable x instead. Finally, cmd | getline pipes the
output of cmd into getline; each call of getline returns the next line
of output from cmd. In all cases, getline returns 1 for a successful
input, 0 for end of file, and -1 for an error.
Patterns are arbitrary Boolean combinations (with ! || &&) of regular
expressions and relational expressions. Regular expressions are as
defined in re_format(7). Isolated regular expressions in a pattern
apply to the entire line. Regular expressions may also occur in rela-
tional expressions, using the operators ~ and !~. /re/ is a constant
regular expression; any string (constant or variable) may be used as a
regular expression, except in the position of an isolated regular
expression in a pattern.
A pattern may consist of two patterns separated by a comma; in this
case, the action is performed for all lines from an occurrence of the
first pattern though an occurrence of the second.
A relational expression is one of the following:
expression matchop regular-expression
expression relop expression
expression in array-name
(expr,expr,...) in array-name
where a relop is any of the six relational operators in C, and a
matchop is either ~ (matches) or !~ (does not match). A conditional is
an arithmetic expression, a relational expression, or a Boolean combi-
nation of these.
The special patterns BEGIN and END may be used to capture control
before the first input line is read and after the last. BEGIN and END
do not combine with other patterns.
Variable names with special meanings:
CONVFMT
conversion format used when converting numbers (default %.6g)
FS regular expression used to separate fields; also settable by
option -Ffs.
NF number of fields in the current record
NR ordinal number of the current record
FNR ordinal number of the current record in the current file
FILENAME
the name of the current input file
RS input record separator (default newline)
OFS output field separator (default blank)
ORS output record separator (default newline)
OFMT output format for numbers (default %.6g)
SUBSEP separates multiple subscripts (default 034)
ARGC argument count, assignable
ARGV argument array, assignable; non-null members are taken as file-
names
ENVIRON
array of environment variables; subscripts are names.
Functions may be defined (at the position of a pattern-action state-
ment) thus:
function foo(a, b, c) { ...; return x }
Parameters are passed by value if scalar and by reference if array
name; functions may be called recursively. Parameters are local to the
function; all other variables are global. Thus local variables may be
created by providing excess parameters in the function definition.
EXAMPLES
length($0) > 72
Print lines longer than 72 characters.
{ print $2, $1 }
Print first two fields in opposite order.
BEGIN { FS = ",[ \t]*|[ \t]+" }
{ print $2, $1 }
Same, with input fields separated by comma and/or blanks and
tabs.
{ s += $1 }
END { print "sum is", s, " average is", s/NR }
Add up first column, print sum and average.
/start/, /stop/
Print all lines between start/stop pairs.
BEGIN { # Simulate echo(1)
for (i = 1; i < ARGC; i++) printf "%s ", ARGV[i]
printf "\n"
exit }
SEE ALSO
lex(1), sed(1)
A. V. Aho, B. W. Kernighan, P. J. Weinberger, The AWK Programming Lan-
guage, Addison-Wesley, 1988. ISBN 0-201-07981-X
BUGS
There are no explicit conversions between numbers and strings. To
force an expression to be treated as a number add 0 to it; to force it
to be treated as a string concatenate "" to it.
The scope rules for variables in functions are a botch; the syntax is
worse.
AWK(1)