Set variable in current shell from awk

Question

Is there a way to set a variable in my current shell from within awk?

I\'d like to do some processing on a file and print out some data; since I\'ll rea

Answer 1

echo "First arg: $1" for ((i=0 ; i < $1 ; i++)); do echo "inside" echo "Welcome $i times." cat man.xml | awk '{ x[NR] = $0 } END { for ( i=2 ; i<=NR ; i++ ) { if (x[i] ~ // ) {x[i+1]=" '$i'"}print x[i] }} ' > $i.xml done echo "compleated"

Answer 2

Make awk print out the assignment statement:

MYVAR=NewValue

Then in your shell script, eval the output of your awk script:

eval $(awk ....)
# then use $MYVAR

EDIT: people recommend using declare instead of eval, to be slightly less error-prone if something other than the assignment is printed by the inner script. It's bash-only, but it's okay when the shell is bash and the script has #!/bin/bash, correctly stating this dependency.

The eval $(...) variant is widely used, with existing programs generating output suitable for eval but not for declare (lesspipe is an example); that's why it's important to understand it, and the bash-only variant is "too localized".

Answer 3

Here's another way.

This is especially useful when when you've got the values of your variables in a single variable and you want split them up. For example, you have a list of values from a single row in a database that you want to create variables out of.

val="hello|beautiful|world" # assume this string comes from a database query
read a b c <<< $( echo ${val} | awk -F"|" '{print $1" "$2" "$3}' )

echo $a #hello
echo $b #beautiful
echo $c #world

We need the 'here string' i.e <<< in this case, because the read command does not read from a pipe and instead reads from stdin

Answer 4

To synthesize everything here so far I'll share what I find is useful to set a shell environment variable from a script that reads a one-line file using awk. Obviously a /pattern/ could be used instead of NR==1 to find the needed variable.

# export a variable from a script (such as in a .dotfile)
declare $( awk 'NR==1 {tmp=$1} END {print "SHELL_VAR=" tmp}' /path/to/file )
export SHELL_VAR

This will avoid a massive output of variables if a declare command is issued with no argument, as well as the security risks of a blind eval.

Answer 5

$ echo "$var"

$ declare $( awk 'BEGIN{print "var=17"}' )
$ echo "$var"
17

Here's why you should use declare instead of eval:

$ eval $( awk 'BEGIN{print "echo \"removing all of your files, ha ha ha....\""}' )
removing all of your files, ha ha ha....

$ declare $( awk 'BEGIN{print "echo \"removing all of your files\""}' )
bash: declare: `"removing': not a valid identifier
bash: declare: `files"': not a valid identifier

Note in the first case that eval executes whatever string awk prints, which could accidentally be a very bad thing!

Answer 6

You can't export variables from a subshell to its parent shell. You have some other choices, though, including:

1. Make another pass of the file using AWK to count records, and use command substitution to capture the result. For example:

   FNR=$(awk 'END {print FNR}' filename)
   

2. Print FNR in the subshell, and parse the output in your other process.
3. If FNR is the same as number of lines, you can call wc -l < filename to get your count.