In a bash shell script, writing a for loop that iterates over string values

In bash, I know that it is possible to write a for loop in which some loop control variable i iterates over specified integers. For example, I can write a bash shell script that prints the integers between 1 and 10:

#!/bin/bash

for i in {1..10}
do
 echo $i
done

Is it possible to instead iterate over a loop control variable that is a string, if I provide a list of strings? For example, suppose that I have a string fname that represents a file name. I want to call a set of commands for each file name. For example, I might want to print the contents of fname using a command like this:

#!/bin/bash

for fname in {"a.txt", "b.txt", "c.txt"}
do
 echo $fname
done

In other words, on the first iteration, fname should have the value fname="a.txt", while on the second iteration, fname should have the value fname="b.txt", and so on. Unfortunately, it seems that the above syntax is not quite correct. I would like to obtain the output:

a.txt

b.txt

c.txt

but when I try the above code, I obtain this output:

{a.txt,

b.txt,

c.txt}

Can you please help me determine the correct syntax, so that I can iteratively change the value/contents of the variable fname? Thank you for your time.

Answers:

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Method 1

The correct syntax is as follows:

#!/bin/bash

for fname in a.txt b.txt c.txt
do
  echo $fname
done

Method 2

Seems to me you should just do…

printf %s.txt\n a b c

Method 3

As noted by user13742 in the comments, we can make use of arrays in bash and ksh:

#!/usr/bin/env bash

files_list=( "a.txt" "b.txt" "c and space.txt" )

for i in "${files_list[@]}"
do
    echo "$i"
    # do something else here,maybe
done

And works as so:

$ ./iterate_files_array.sh                                                      
a.txt
b.txt
c and space.txt

However, some shells such as dash ( /bin/sh on Ubuntu ) don’t support arrays. In such case we could resort to using here-document structure: <<

#!/bin/sh

while IFS= read -r line
do
    echo "$line"
done << EOL
one.txt
two.txt
with space.txt
EOL

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0