Replace a string based on input

Shell Programming and Scripting
1

I am trying to read a value from a mapping file and would need to replace the value based on country parameter

source_table_@ctry_final
Expected
final_var=source_table_aus_final

If the country is in nz,usa,uk then 
final_var=diff_table_nz_final
final_var=diff_table_usa_final
like that

else
final_var=source_table_aus_final

My try


final_var=$(echo "source_table_@ctry_final"| sed -e "s/\@ctry/${ctry_input}/")
2

Please state the operating system, including version, and the shell you are using.

This works in ksh93 (Version AJM 93u+ 2012-08-01) on Ubuntu 18.04.3 LTS:

$ src=source_table_@ctry_final
$ rplst=nz,usa,uk
$ echo ${src/@ctry/{$rplst}}
source_table_nz_final source_table_usa_final source_table_uk_final

Strangely enough, it doesn't work with bash (4.4.20(1)-release):

$ echo ${src/ctry/{$rplst}}
source_table_{nz,usa,uk_final}

If anybody knows why, could we start a new thread on this, uh, feature?
[..]

3

In bash , the unloved, deprecated eval helps:

eval echo ${src/@ctry/{$rplst\}}
 source_table_nz_final source_table_usa_final source_table_uk_final

and, no, the $ and { need to be in that sequence in order to make it a "brace expansion", which, in turn, can only be recognized / evaluated by the evil eval .

1 Like
4

But expected would be below. source string needs to be replaced with diff

diff_table_usa_final

Shell is bash

5

How is that "country parameter" supplied and evaluated?

The @ctry part has which value, for _aus_ to be part of the final string?

Which table is relevant - diff_table or source_table - or is the distinction part of the problem?

What is and which value has ctry_input ? Where does it come into play?

6

It is because of the parsing order of the shell. In bash brace expansions are performed before any of the other expansions, hence the need for eval (usual caution applies (security)!) for a second round of expansions after the first round.

7

Unlike bash, ksh93 seems to do variable expansion before brace expansion. (Scrutinizer just said it.)

Master_Mind, I am not fully getting your requirement, but here is how you can adjust the ctry_input variable

#!/bin/sh
ctry_input=$1
case $ctry_input in
nz|usa|uk)
;;
*)
  ctry_input=aus
;;
esac
sed "s/@ctry/$ctry_input/"

This sample script you can run with a "uk" or "usa" argument, for example

sh sample.sh uk < inputfile

--- Post updated at 12:39 ---

To meet your sourc/diff replacement requirement, you can move the sed into the case-branch:

#!/bin/sh
ctry_input=$1
case $ctry_input in
nz|usa|uk)
  sed "s/@ctry/$ctry_input/
  s/source_table/diff_table/"
;;
*)
  ctry_input=aus
  sed "s/@ctry/$ctry_input/"
;;
esac
8

Not sure (as your requirement is still unclear) if this one, using recent bash 's extglob option and some "parameter expansions", gets you somewhere:

shopt -s extglob
rplst="nz|usa|uk"
for ctry in de nz usa uk aus aut nl
  do    VLD=${ctry/${ctry/@($rplst)}} 
        SD=${VLD:+diff}
        final_var=${SD:-source}_table_${VLD:-aus}_final
        echo $final_var
done
source_table_aus_final
diff_table_nz_final
diff_table_usa_final
diff_table_uk_final
source_table_aus_final
source_table_aus_final
source_table_aus_final
9

Let me be clear once again as per below code, i am getting ctry_input as input to my shell program. Where in if i get countries like nz,usa,uk then source should be replaced as diff

diff_table_nz_final

Apart from nz,usa,uk it should be

source_table_<any_other_country>_final

any_other_country if eg if i pass as aus then it would source_table_aus_final

final_var=$(echo "source_table_@ctry_final"| sed -e "s/\@ctry/${ctry_input}/")

Basically would need to tweak the above code

10 
for ctry in de nz usa uk aus aut nl
  do    VLD=${ctry/${ctry/@($rplst)}} 
        SD=${VLD:+diff}
        final_var=${SD:-source}_table_${ctry}_final
        echo $final_var
done
source_table_de_final
diff_table_nz_final
diff_table_usa_final
diff_table_uk_final
source_table_aus_final
source_table_aut_final
source_table_nl_final
11

Thanks RudiC for your help. But is there a way to tweak the existing code itself

final_var=$(echo "source_table_@ctry_final"| sed -e "s/\@ctry/${ctry_input}/")

why i am saying is because you if i give other than in that case only ctry only needs to be replaced

echo "other_table_@ctry_final"

I am trying to achieve madeingermany's method

final_var=$(echo "source_table_@ctry_final" | case $ctry_input in nz|usa|uk) sed "s/@ctry/$ctry_input/s/source_table/diff_table/";;*) sed "s/@ctry/$ctry_input/" ;; esac )