[Perl] Find one string, change another string.

Shell Programming and Scripting
1

Hi,

In principle I am searching for a Perl equivalent for this sed command:

sed "/TIM_AM_ARGS=/ s/60/1440/" $EDIT_FILE > $TEMP_FILE
cp $TEMP_FILE $EDIT_FILE

I was wondering if it needs to be like this, or that there other, shorter, alternatives:

open (TIMENVFILE, "<$timenvfile") or die "Cannot open $timenvfile\n";
my @lines = <TIMENVFILE>;
close (TIMENVFILE);

open (NEWTIMENVFILE, ">$timenvfile")  or die "Cannot open $timenvfile\n";
for (@lines) {
  if ( $_ =~ m/TIM_AM_ARGS/ ) { $_ =~ s/60/1440/}
  print NEWTIMENVFILE;
  }
close (NEWTIMENVFILE);

This is part of the file:

export TIM_ALMSRV_ARGS
TIM_AM_ARGS="-S -U 1440 nbsol151alarms"

I am mostly interested in this part of the code:

if ( $_ =~ m/TIM_AM_ARGS/ ) { $_ =~ s/60/1440/}

It is a one-liner, but perhaps there is a better way of doing it.

E.J.

2

you could write a perl one-liner for this. but if you are still interested in a perl script, here's one:

#!/usr/bin/perl
# sed_like.pl
use strict
use warnings;

my $filename = shift;
my $newfile  = shift;

my @to_write;
open(FREAD, '<', $filename)  or  die "Failed to read file $filename : $!";
while (<FREAD>) {
    if (m/TIM_AM_ARGS=/) {
        s/60/1440/;    # may be you need word boundaries here? like this: s/\b60\b/1440/
    }
    push(@to_write, $_);
}
close(FREAD);

open(FWRITE, '>', $newfile)  or  die "Failed to write file $newfile : $!";
print FWRITE @to_write;
close(FWRITE);

run this perl script as:

perl sed_like.pl file.txt newfile.txt

edit: and here's the one-liner:

perl -pi -e 's/60/1440/  if (/TIM_AM_ARGS=/)' file.txt
3

Thanks.
So the if statement is okay this way, I assume.

Just out of interest, what is the difference between a perl one-liner and a perl script ?
Basically a one-liner is a script consisting of one line (which can be run from the command line with perl -e).
Or ?

E.J.

4

Hi.

Most perl installations include s2p, a sed-to-perl translator. Here is an example:

#!/usr/bin/env bash

# @(#) s1	Demonstrate sed-to-perl translator, s2p.

echo
set +o nounset
LC_ALL=C ; LANG=C ; export LC_ALL LANG
echo "Environment: LC_ALL = $LC_ALL, LANG = $LANG"
echo "(Versions displayed with local utility \"version\")"
version >/dev/null 2>&1 && version "=o" $(_eat $0 $1) sed s2p
set -o nounset
echo

FILE=${1-data1}

echo " Data file $FILE:"
cat $FILE

echo
echo " Results:"
lines=$( s2p -f $FILE | wc -l )

echo " The s2p translator produced $lines lines of perl."

exit 0

producing:

% ./s1

Environment: LC_ALL = C, LANG = C
(Versions displayed with local utility "version")
OS, ker|rel, machine: Linux, 2.6.26-2-amd64, x86_64
Distribution        : Debian GNU/Linux 5.0 
GNU bash 3.2.39
GNU sed version 4.1.5
s2p - ( /usr/bin/s2p Jan 1 09:56 )

 Data file data1:
/TIM_AM_ARGS=/ s/60/1440/

 Results:
 The s2p translator produced 122 lines of perl.

See man s2p for details ... cheers, drl

5

The biggest difference is that a script is generally saved as a file and a one-liner isn't.

A one-liner can actually be more than one line. They are generally used for simple tasks, where a script can do much more complex stuff than you would typically want to try using a one-liner.

6

Thanks for pointing out the sed-to-perl translator.
I had a look at the output, but 122 lines of Perl ?
Better stick with what I had.

Thanks for responding.

E.J.