linux - [Solved-5 Solutions] How to use shell variables in an awk script in Linux ? - ubuntu - red hat - debian - linux server - linux pc

How to use shell variables in an awk script in Linux ?

Here is the best way to do it. It uses the -v option: (P.S. use a space after -v or it will be less portable. E.g., awk -v var= not awk -vvar)

variable="line one\nline two"
awk -v var="$variable" 'BEGIN {print var}'
line one
line two

This should be compatible with most awk and variable is available in the BEGIN block as well:

variable="line one\nline two"
awk 'BEGIN {print "'"$variable"'"}'
line one
line two

Here is an example of code injection:

variable='line one\nline two" ; for (i=1;i<=1000;++i) print i"'
awk 'BEGIN {print "'"$variable"'"}'
line one
line two
1
2
3
.
.
1000

You can add lots of commands to awk this way. Even make it crash with non valid commands.

Here we get the variable after the awk code. This will work fine as long as you do not need the variable in the BEGIN block:

variable="line one\nline two"
echo "input data" | awk '{print var}' var="$variable"
or
awk '{print var}' var="$variable" file

Variable can also be added to awk using here string

awk '{print $0}' <<< "$variable"
test

This is the same as:

echo "$variable" | awk '{print $0}'

It's always good to double quote variable "$variable" If not, multiple lines will be added as a long single line.

var="Line one
This is line two"

echo $var
Line one This is line two

echo "$var"
Line one
This is line two

Other errors you can get without double quote:

variable="line one\nline two"
awk -v var=$variable 'BEGIN {print var}'
awk: cmd. line:1: one\nline
awk: cmd. line:1:    ^ backslash not last character on line
awk: cmd. line:1: one\nline
awk: cmd. line:1:    ^ syntax error

And with single quote, it does not expand the value of the variable:

awk -v var='$variable' 'BEGIN {print var}'
$variable

As TrueY write, you can use the ENVIRON to print Environmental Variables Setting a variable before running AWK, you can print it out like this:

X=MyVar awk 'BEGIN{print ENVIRON["X"],ENVIRON["SHELL"]}'
MyVar /bin/bash

It seems that the good-old ENVIRON awk built-in hash is not mentioned at all. For Example:

$ X=Solaris awk 'BEGIN{print ENVIRON["X"], ENVIRON["TERM"]}'
Solaris rxvt

Use either of these depending how you want backslashes in the shell variables handled :

awk -v avar="$svar" '... avar ...' file
awk 'BEGIN{avar=ARGV[1];ARGV[1]=""}... avar ...' "$svar" file

You could pass in the command-line option -v with a variable name (v) and a value (=) of the environment variable ("${v}"):

% awk -vv="${v}" 'BEGIN { print v }'
123test

Or to make it clearer:

% environment_variable=123test
% awk -vawk_variable="${environment_variable}" 'BEGIN { print awk_variable }'
123test

To insert date at the beginning of the lines of a log file and it's done like below:

DATE=$(date +"%Y-%m-%d")
awk '{ print "'"$DATE"'", $0; }' /path_to_log_file/log_file.log