Replacing text strings in bash using awk

Question

I have a list of files in bash - file1.txt, file2.txt, file3.txt and I would like to make another list that include this strings without .txt, so

names2 = (file1, file2, file3)

Then, I would like to find these strings in a file and add a before this strings. How to do that please?

My Code:

names = (file1.txt, file2.txt, file3.txt)

for i in "${names[@]}"; do
    awk '{ gsub("$i","a-$i") }' f.txt > g.txt

f.txt:

TEXT
\connect{file1}
\begin{file2}
\connect{file3}
TEXT 
75

Desired output g.txt

TEXT
\connect{a-file1}
\begin{a-file2}
\connect{a-file3}
TEXT 
75

Answer 1

With sed+printf:

$ names=(file1 file2 file3) # Declare array

$ printf 's/%s/a-&/g\n' "${names[@]}" # Generate sed replacement script
s/file1/a-&/g
s/file2/a-&/g
s/file3/a-&/g

$ sed -f <(printf 's/%s/a-&/g\n' "${names[@]}") f.txt
TEXT
\connect{a-file1}
\begin{a-file2}
\connect{a-file3}
TEXT
75

If your array contains .txt suffix, use this:

$ names=(file1.txt file2.txt file3.txt) # Declare array

$ printf 's/%s/a-&/g\n' "${names[@]%.txt}" # Generate sed replacement script
s/file1/a-&/g
s/file2/a-&/g
s/file3/a-&/g

$ sed -f <(printf 's/%s/a-&/g\n' "${names[@]%.txt}") f.txt
TEXT
\connect{a-file1}
\begin{a-file2}
\connect{a-file3}
TEXT
75

If the files list contains the names which have overlapping string, you can use the word boundaries (\<,\>) to handle this. e.g.

$ cat f.txt
TEXT
\connect{file1}
\begin{file2}
\connect{file3file2}
TEXT 
75

$ names=(file1.txt file2.txt file3file2.txt) # Declare array
$ printf 's/\<%s\>/a-&/g\n' "${names[@]%.txt}" # Generate sed replacement script
s/\<file1\>/a-&/g
s/\<file2\>/a-&/g
s/\<file3file2\>/a-&/g

$ sed -f <(printf 's/\<%s\>/a-&/g\n' "${names[@]%.txt}") f.txt
TEXT
\connect{a-file1}
\begin{a-file2}
\connect{a-file3file2}
TEXT 
75

Answer 2

Could you please try following.

Variable with values in shell:

string="file1.txt, file2.txt, file3.txt"

Creating a shell array as follows:

IFS=', ' read -r -a array <<< "$string"

OR if you want to stick with your way of defining array then do like:

array=(file1.txt file2.txt file3.txt)

Passing above shell created array to awk and reading Input_file for doing the final operations.

awk -v arr="${array[*]}" '
BEGIN{
  FS=OFS="{"
  num=split(arr,array," ")
  for(i=1;i<=num;i++){
    sub(/\.txt/,"",array[i])
    array1[array[i]"}"]
  }
}
$2 in array1{
  $2="a-"$2
}
1
'  Input_file

Explanation: Adding explanation of above code here.

awk -v arr="${array[*]}" '       ##Creating a variable named arr whose value is all elements of array(shell array).
BEGIN{                           ##Starting BEGIN section of awk code here.
  FS=OFS="{"                     ##Setting FS and OFS as { here.
  num=split(arr,array," ")       ##Splitting arr variable into array named array with delimiter space and its length is stored in num variable.
  for(i=1;i<=num;i++){           ##Starting for loop from i=1 to till value of variable num.
    sub(/\.txt/,"",array[i])     ##Using sub to substitute .txt with NULL in array value whose index is variable named i.
    array1[array[i]"}"]          ##Creating an array1 whose index is array[i] value with } in it.
  }                              ##Closing for loop here.
}                                ##Closing BEGIN section of code here.
$2 in array1{                    ##Checking condition if $2 of current line is present in array named array1 then do following.
  $2="a-"$2                      ##Adding string a- with value of $2.
}                                ##Closing BLOCK for condition here.
1                                ##Mentioning 1 will print edited/non-edited line of Input_file.
'  Input_file                    ##Mentioning Input_file name here.