Creation of files with control of the names - linux

Question

I have n files, named f1, f2, ..., fn. For each of these files, I have to execute a sed command, and name the new files as file1, file2, ..., filen.
I need the new files to keep the same number as their original ones. Can anyone help?
Here's what I've tried so far:
#!/bin/sh
for element in *
do
echo "$element" sed -n '/Col3/p' $element > Quest $element
done

Answer 1

If we assume that all the your files are in the form in your question...
$ ls -l
total 2
-rw-r--r-- 1 ghoti wheel 0 Jan 3 13:20 f1
-rw-r--r-- 1 ghoti wheel 0 Jan 3 13:20 f2
-rw-r--r-- 1 ghoti wheel 0 Jan 3 13:20 f3
-rw-r--r-- 1 ghoti wheel 0 Jan 3 13:20 f4
then you're on the right track with a for loop. But you probably want to narrow your search to only the files that are important to you.
In bash, you can use extglob to control this sort of thing. For example:
#!/usr/bin/env bash
shopt -s extglob
for file in +([a-z])+([0-9]); do
echo "Old: $file / New: file${file##[a-z]}"
done
This matches any files whose names consist of letters followed by numbers.
If, on the other hand, you want to make this portable, so that it will work in a POSIX shell (since in your question you've specified /bin/sh), you might put the detection into the loop itself:
#!/bin/sh
for file in *; do
if ! expr "$file" : '[a-z][a-z]*[0-9][0-9]*$' >/dev/null; then
continue
fi
echo "Old: $file / New: file${file##[a-z]}"
done
In both of these examples, we use POSIX "Parameter Expansion" to strip off the letters at the beginning of the filename.

Answer 2

#!/bin/env bash
for FILE in *
do
[[ "$FILE" =~ [0-9]+$ ]] && mv "$FILE" file${BASH_REMATCH[0]}
done
The expression within [[ ]] is a test, which tests for a match against a regular expression, which looks for a string ending in a number. If the match is successful, the matched number can be found in the bash array variable BASH_REMATCH at index 0. The part after && is executed if the test succeeds, and renames the file to fileNN,