Append wc lines to filename

find -name '*.txt' -execdir bash -c \  'mv -v "$0" "${0%.txt}_$(wc -l < "$0").txt"' {} \;

where

• the bash command is executed for each (\;) matched file;
• {} is replaced by the currently processed filename and passed as the first argument ($0) to the script;
• ${0%.txt} deletes shortest match of .txt from back of the string (see the official Bash-scripting guide);
• wc -l < "$0" prints only the number of lines in the file (see answers to this question, for example)

Sample output:

'./file-a.txt' -> 'file-a_5.txt''./file with spaces.txt' -> 'file with spaces_8.txt'

You could use the rename command, which is actually a Perl script, as follows:

rename --dry-run 'my $fn=$_; open my $fh,"<$_"; while(<$fh>){}; $_=$fn; s/.txt$/-$..txt/' *txt

Sample Output

'tight_layout1.txt' would be renamed to 'tight_layout1-519.txt''tight_layout2.txt' would be renamed to 'tight_layout2-1122.txt''tight_layout3.txt' would be renamed to 'tight_layout3-921.txt''tight_layout4.txt' would be renamed to 'tight_layout4-1122.txt'

If you like what it says, remove the --dry-run and run again.

The script counts the lines in the file without using any external processes and then renames them as you ask, also without using any external processes, so it quite efficient.

Or, if you are happy to invoke an external process to count the lines, and avoid the Perl method above:

rename --dry-run 's/\.txt$/-`grep -ch "^" "$_"` . ".txt"/e' *txt

Use rename command

for file in *.txt; do  lines=$(wc ${file} | awk {'print $1'}); rename s/$/${lines}/ ${file}done