I found some ways to pass external shell variables to an
awk
'
"
$ v=123test
$ echo $v
123test
$ echo "$v"
123test
$ awk 'BEGIN{print "'$v'"}'
$ 123test
$ awk 'BEGIN{print '"$v"'}'
$ 123
$ awk 'BEGIN{print " '$v' "}'
$ 123test
$ awk 'BEGIN{print ' "$v" '}'
awk: cmd. line:1: BEGIN{print
awk: cmd. line:1: ^ unexpected newline or end of string
Getting shell variables into awk
may be done in several ways. Some are better than others.
This is the best way to do it. It uses the -v
option: (P.S. use a space after -v
or it will be less portable. E.g., awk -v var=
not awk -vvar
)
variable="line one\nline two"
awk -v var="$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:
You can use a variable within the awk
code, but it's messy and hard to read, and as Charles Duffy
points out, this version may also be a victim of code injection. If someone adds bad stuff to the variable, it will be executed as part of the awk
code, so DO NOT USE.
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.
Example:
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