passing variable from bash to perl in a bash script
 

Hello,


I need to find the first position of an exact substring (not a regular expression) inside a substring and bash is not adequate.

For example in the following bash snippet, 1 will be echoed because the first position of either "a" or "t" in "adequate" is 1 :

#!/bin/bash
MYVARIABLE="adequate"
POSITION=`expr index "$MYVARIABLE" at`
echo $POSITION
exit



I could embed the following Perl in my bash script:

#!/bin/bash
echo "Index value is..."

# Embedded Perl script.
POSITION=`perl -e 'print index("Once upon a time","im");'`

echo $POSITION
exit



Now the problem:

How do I replace "Once upon a time" and "im" in the embedded Perl line with bash variables? I need to do:


#!/bin/bash

MYVARIABLE="adequate"
MYSUBSTRING="at"

# Embedded Perl script.
POSITION=`perl -e 'print index($MYVARIABLE,$MYSUBSTRING);'`

echo $POSITION
exit

Missing quotes, no?
Try:
POSITION=`perl -e 'print index("$MYVARIABLE","$MYSUBSTRING");'`

Nope
 

Nope, the following will echo "0"


#!/bin/bash

MYVARIABLE="adequate"
MYSUBSTRING="at"

# Embedded Perl script.
POSITION=`perl -e 'print index("$MYVARIABLE","$MYSUBSTRING");'`

echo $POSITION
exit

single-quote works
 

The following works, echoing "5":

#!/bin/bash

MYVARIABLE="adequate"
MYSUBSTRING="at"

# Embedded Perl script.
POSITION=`perl -e 'print index('$MYVARIABLE','$MYSUBSTRING');'`

echo $POSITION
exit

Hi.

Double quotes will work:
To produce:
I placed the quotes around the perl snippet, and the shell evaluated the variables inside. I recommend the alternate syntax for backquotes:
because they nest more easily, and are more visually apparent ... cheers, makyo

( edit 1: add, clarify )

why not do the whole problem in perl?

Inspired by awk code.
 

For awk who want to use bash variable:
awk -F" " {'if ($2=="'${BASH_VAR}'") print $7'}

For Perl who want to use bash variable:
###############
Actually, it's bash's job to expand ${BASH_VAR} rather than perl. These code explain a lot.

BTW: I do love 'perl -ne'