Search and replace in a file using expressions from another file

[louisJ]

Hi

I would like to search in replace expressions in a text file (target file), using expressions from another text file (expressions file) that looks like this:
stringtosearch1 [tab] replacementstring1
stringtosearch2 [tab] replacementstring2
stringtosearch3 [tab] replacementstring3
...

Can somebody help me on this?
Thanks.

[atreyu]

If your "expressions-file.txt" file looks like this:

stringy1        shiny1
stringy2        shiny2
stringy3        shiny3

and your "target-file.txt" file looks something like this:

stringy0
stringy1
foo 
stringy2
bar 
stringy3
blah

You could try this:

#!/bin/bash

# define location of the two required files
exprFile=./expressions-file.txt
targFile=./target-file.txt
for file in $expressionsFile $targetFile; do
  ! [ -f $file ] && echo $file: No such file && exit 1
done

# iterate over the expressions file, line by line
cat $exprFile|while read line; do

  # store columnar date in an array
  declare -a array
  array=($echo $line)

  # make sure exactly two columns of data are provided on each line
  if [ ${#array[*]} -ne 2 ]; then
    echo "Need exactly two columns - skipping line"
    continue
  fi

  search=${array[0]}
  replace=${array[1]}

  # do the inline replacement with sed, saving to a backup file
#  echo replacing $search with $replace in $targFile..
  sed -i.bak s/$search/$replace/g $targFile

done

It should output this:

stringy0
shiny1
foo
shiny2
bar
shiny3
blah

[louisJ]

Thanks a lot!

Will it work with a file with various format of text and sentences like this:

Stringy0, blabla stringy1. Bfoo stringy2 ar   stringy3 blah; blablablabla.

Can I make it case sensitive?

Thank you.

[drl]

Hi.

An alternative is to transform the pattern file into sed substitution expressions and use sed to read the resulting pattern file, applying the changes to a main data file. Here is a sample script that displays the context, the strings file, the resulting patterns file, the main data file and the final file with old strings replaced by new strings:

#!/usr/bin/env bash

# @(#) s1	Demonstrate creation and execution of sed script.

# Utility functions: print-as-echo, print-line-with-visual-space, debug.
# export PATH="/usr/local/bin:/usr/bin:/bin"
pe() { for _i;do printf "%s" "$_i";done; printf "\n"; }
pl() { pe;pe "-----" ;pe "$*"; }
db() { ( printf " db, ";for _i;do printf "%s" "$_i";done;printf "\n" ) >&2 ; }
db() { : ; }
C=$HOME/bin/context && [ -f $C ] && . $C sed

r=data2
m=data1

pl " Input data file, replacements, $r:"
cat $r

pl " Results of creating pattern file:"
rm -f patterns
sed 's|\(.*\)\t\(.*\)|s/\1/\2/g|' $r |
tee patterns

pl " Main data file $m:"
cat $m

pl " Results of applying pattern file with sed to main data file:"
sed -f patterns $m

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 5.0.8 (lenny) 
GNU bash 3.2.39
GNU sed version 4.1.5

-----
 Input data file, replacements, data2:
stringy1	shiny1
stringy2	shiny2
stringy3	shiny3

-----
 Results of creating pattern file:
s/stringy1/shiny1/g
s/stringy2/shiny2/g
s/stringy3/shiny3/g

-----
 Main data file data1:
stringy0
stringy1
foo 
stringy2
bar 
stringy3
blah
Stringy0, blabla stringy1. Bfoo stringy2 ar   stringy3 blah; blablablabla.

-----
 Results of applying pattern file with sed to main data file:
stringy0
shiny1
foo 
shiny2
bar 
shiny3
blah
Stringy0, blabla shiny1. Bfoo shiny2 ar   shiny3 blah; blablablabla.

The advantage to this extra work is that there needs to be only a single pass over the main data file. For small data files and a small number of replacements there probably is not much of a gain.

Best wishes ... cheers, drl

[atreyu]

Will it work with a file with various format of text and sentences like this:

Stringy0, blabla stringy1. Bfoo stringy2 ar   stringy3 blah; blablablabla.

Well, the short answer is yes, you can do pretty much whatever text mangling you can imagine with awk/sed/grep (or perl!). But I don't understand what you want, based upon the example file you gave. Is it an example of the expressions file or the target file?

Can I make it case sensitive?

It already is! By default, "Linux is case-sensitive". You'd make this script case-insensitive by tacking on the i switch to the sed command (after the /g).

[louisJ]

Atreyu it was the target file.
But you pretty much answerd the question.

Thanks to both of you Drl and Atreyu for helping.