Linux: (g) awk – search and replace.
awk or gawk (gnu awk)
Find and Replace text, database sort/validate/index
Syntax
awk <options> 'Program' Input-File1 Input-File2 ...
awk -f PROGRAM-FILE <options> Input-File1 Input-File2 ...
Key
-F FS
--field-separator FS
Use FS for the input field separator (the value of the `FS'
predefined variable).
-f PROGRAM-FILE
--file PROGRAM-FILE
Read the `awk' program source from the file PROGRAM-FILE, instead
of from the first command line argument.
-mf NNN
-mr NNN
The `f' flag sets the maximum number of fields, and the `r' flag
sets the maximum record size. These options are ignored by
`gawk', since `gawk' has no predefined limits; they are only for
compatibility with the Bell Labs research version of Unix `awk'.
-v VAR=VAL
--assign VAR=VAL
Assign the variable VAR the value VAL before program execution
begins.
-W traditional
-W compat
--traditional
--compat
Use compatibility mode, in which `gawk' extensions are turned off.
-W lint
--lint
Give warnings about dubious or non-portable `awk' constructs.
-W lint-old
--lint-old
Warn about constructs that are not available in the original
Version 7 Unix version of `awk'.
-W posix
--posix
Use POSIX compatibility mode, in which `gawk' extensions are
turned off and additional restrictions apply.
-W re-interval
--re-interval
Allow interval expressions, in regexps.
-W source=PROGRAM-TEXT
--source PROGRAM-TEXT
Use PROGRAM-TEXT as `awk' program source code. This option allows
mixing command line source code with source code from files, and is
particularly useful for mixing command line programs with library
functions.
--
Signal the end of options. This is useful to allow further
arguments to the `awk' program itself to start with a `-'. This
is mainly for consistency with POSIX argument parsing conventions.
'Program'
A series of patterns and actions: see below
Input-File
If no Input-File is specified then `awk' applies the Program to
"standard input", (piped output of some other command or the terminal.
Typed input will continue until end-of-file (typing `Control-d')
Basic functions
The basic function of awk is to search files for lines (or other units of text) that contain a pattern. When a line matches, awk performs a specific action on that line.
The Program statement that tells `awk’ what to do; consists of a series of “rules”. Each rule specifies one pattern to search for, and one action to perform when that pattern is found.
For ease of reading, each line in an `awk’ program is normally a separate Program statement , like this:
pattern { action }
pattern { action }
...
e.g. Display lines from my_file containing the string “123″ or “abc” or “some text”:
awk '/123/ { print $0 }
/abc/ { print $0 }
/some text/ { print $0 }' my_file
A regular expression enclosed in slashes (`/’) is an `awk’ pattern that matches every input record whose text belongs to that set. e.g. the pattern /foo/ matches any input record containing the three characters `foo’, *anywhere* in the record.
`awk’ patterns may be one of the following:
/Regular Expression/ - Match = Pattern && Pattern - AND Pattern || Pattern - OR ! Pattern - NOT Pattern ? Pattern : Pattern - If, Then, Else Pattern1, Pattern2 - Range Start - end BEGIN - Perform action BEFORE input file is read END - Perform action AFTER input file is read
In addition to simple pattern matching `awk’ has a huge range of text and arithmetic Functions, Variables and Operators.
`gawk’ will ignore newlines after any of the following:
, { ? : || && do else
Comments – start with a `#’, and continue to the end of the line:
# This program prints a nice friendly message
Examples
This program prints the length of the longest input line:
awk '{ if (length($0) > max) max = length($0) }
END { print max }' data
This program prints every line that has at least one field. This is an easy way to delete blank lines from a file (or rather, to
create a new file similar to the old file but from which the blank lines have been deleted)
awk 'NF > 0' data
This program prints seven random numbers from zero to 100, inclusive.
awk 'BEGIN { for (i = 1; i <= 7; i++)
print int(101 * rand()) }'
This program prints the total number of bytes used by FILES.
ls -lg FILES | awk '{ x += $5 } ; END { print "total bytes: " x }'
This program prints a sorted list of the login names of all users.
awk -F: '{ print $1 }' /etc/passwd | sort
This program counts lines in a file.
awk 'END { print NR }' data
This program prints the even numbered lines in the data file. If you were to use the expression `NR % 2 == 1′ instead, it would print the odd numbered lines.
awk 'NR % 2 == 0' data
DIGG ME
No Comments »
No comments yet.
RSS feed for comments on this post. TrackBack URL
Leave a comment