mjhjmtu

I have a directory with several files named as follow:

London_qle_merged
Paris_qle_merged
Tokyo_qle_merged
London_qle_obs
Paris_qle_merged
Tokyo_qle_merged

How can I rename the file having *merged in the filename as follow:

London_Qle_merged
Paris_Qle_merged
Tokyo_Qle_merged

I know that I could do a loop as follow:

for name in Paris London Tokyo do;
 mv $name_qle_merged $name_Qle_merged
done

but is there no other way?

Sure. In ksh/Bash/zsh:

for f in *_merged; do
 mv -- "$f" "$f/_qle_/_Qle_" 
done

or in standard shell.

for f in *_qle_merged; do
 mv -- "$f" "$f%_qle_merged_Qle_merged" 
done

See also, e.g. Parameter Expansion in BashGuide

I have done this by combination of awk and tr

Command

find . -type f -iname "*merged" |tr -d "./" | awk -F "_" 'print "mv" " " $1"_"$2"_"$3 " " $1"_"toupper(substr($2,1,1))substr($2,2)"_"$3 ' | sh

Below merged files

London_qle_merged
Paris_qle_merged
Tokyo_qle_merged 

renamed to

London_Qle_merged
Paris_Qle_merged
Tokyo_Qle_merged

This will do the job with no script loops, spawning just a single sub-process:

rename 's/qle/Qle/' *_merged

The rename command is your friend here. It is sed for file names. (ensure that you have the Larry Wall version, there is at least two programs with this name).

The following answer is for file content, and thus uses sed. I have used it and re-purposed it to rename.
https://unix.stackexchange.com/a/211579/4778

rename -e 's/_(.)/_u$1/' *_merged

It up cases the letter immediately following the first _.

A simpler solution for this specific input

rename 's/qle/Qle/' *_merged