How to ask for confirmation using the command `sed` [closed] - linux

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I'm trying to replace a string over multiple files using the command sed like:
grep -rl matchstring somedir/ | xargs sed -i 's/string1/string2/g'
My question is: is there a way to enable it to ask for confirmation at each substitution?
I tried to include the latter c after g in the substitution command, but it didn't succeed.
Thank you in advance for any comments.

Answer 1

The sed utility does not have confirmation ability. If/Until it is implemented, consider using other tools.
The 'ex' (vim in command line mode), has lot of power, including per change confirmation. The confirmation mode is geared toward visual usage. One problem is that once a single change is not approved, the substitution stop. On the surface, this is not what is being asked.
Potentially solution will be to use scripting engine capable of substitutions, and implement a confirmation logic. Awk, Perl, python meet those requirements.
Perl has edit in place option. Script can be invoked with 'perl -i.bak'.
Security: Notice code may need additional protection against injection into RE. See below
Activate:
grep -rl matchstring somedir/ | xargs perl -i.bak sub-conf.pl 'string1' 'string2'
#! /usr/bin/perl
use strict ;
my ($in_pattern, $replacement) = (shift, shift) ;
# Convert string to regexp, disable special characters, etc.
my $pattern = quotemeta($in_pattern) ;
open TTY, "/dev/tty" or die "Failed to open TTY: $!" ;
# Read a line into orig
my $eof ;
while ( my $orig = <> ) {
my $new = $orig =~ s/$pattern/$replacement/gr ;
if ( $new ne $orig ) {
print STDERR "Replace line ${.}:\n< ${orig}> $new" ;
while (1) {
print STDERR "(Y/N) ?" ;
my $yn = <TTY> ;
unless ( defined($yn) ) { $eof = 1 ; last } ;
if ( $yn =~ /[Yy]/ ) { print $new ; last ; } ;
if ( $yn =~ /[Nn]/ ) { print $orig ; last ; } ;
} ;
} else {
print $orig ;
} ;
die 'EOF' if $eof ;
} ;
See: How can I safely validate an untrusted regex in Perl? for explanation of the injection protection in case command need to be extended to accept REGEX.