I have a directory that has a large number of files. These files are named according to the following system: "Var1_X_Var2_Y_Var3_Z_data_N.txt" Where X, Y, and Z are many different numbers, and N ranges from 1 to 30.

To use these files in my next script i need to add a leading zero for files where N is 1 to 9.

On my ubuntu machine I use the following command

rename  's/_1.txt/_01.txt/' *

and repeat it from 1 to 9.
However, this command will not work on a cluster I am using. I need a unix or bash or python alternative.

(note: I know there are many related questions on stackexchange, but all of them seem to use cases in which all the files share the same stem. I have destroyed several files trying to apply those solutions)

2 Answers 2


You want the N in Var1_X_Var2_Y_Var3_Z_data_N.txt to be a zero-filled two-digit integer.

Assuming all affected files matches the pattern *_[0-9].txt:

for name in *_[0-9].txt; do
    stem="${name%.txt}"    # remove the ".txt" suffix
    num=${stem##*_}        # extract the number at the end
    newname="${stem%[0-9]}$( printf '%02d.txt' "$num" )" # put it back together

    printf 'Would rename "%s" into "%s"\n' "$name" "$newname"
    # mv -- "$name" "$newname"
  • ${name%.txt} removes the .txt from the end of $name, the original filename. This creates the "stem", which is not really the stem since it still has the number at the very end.
  • ${stem##*_} removes everything up to and including the last underscore in $stem.
  • ${stem%[0-9]} is the stem without the number at the end (e.g. Var1_X_Var2_Y_Var3_Z_data_).
  • printf '%02d.txt' "$num" produces a zero-filled two-digit number from $num, followed by the string .txt.

Given a directory with the files

Var1_X_Var2_Y_Var3_Z_data_1.txt              Var1_X_Var2_Y_Var3_Z_data_23.txt
Var1_X_Var2_Y_Var3_Z_data_10.txt             Var1_X_Var2_Y_Var3_Z_data_24.txt
Var1_X_Var2_Y_Var3_Z_data_11.txt             Var1_X_Var2_Y_Var3_Z_data_25.txt
Var1_X_Var2_Y_Var3_Z_data_12.txt             Var1_X_Var2_Y_Var3_Z_data_26.txt
Var1_X_Var2_Y_Var3_Z_data_13.txt             Var1_X_Var2_Y_Var3_Z_data_27.txt
Var1_X_Var2_Y_Var3_Z_data_14.txt             Var1_X_Var2_Y_Var3_Z_data_28.txt
Var1_X_Var2_Y_Var3_Z_data_15.txt             Var1_X_Var2_Y_Var3_Z_data_29.txt
Var1_X_Var2_Y_Var3_Z_data_16.txt             Var1_X_Var2_Y_Var3_Z_data_3.txt
Var1_X_Var2_Y_Var3_Z_data_17.txt             Var1_X_Var2_Y_Var3_Z_data_30.txt
Var1_X_Var2_Y_Var3_Z_data_18.txt             Var1_X_Var2_Y_Var3_Z_data_4.txt
Var1_X_Var2_Y_Var3_Z_data_19.txt             Var1_X_Var2_Y_Var3_Z_data_5.txt
Var1_X_Var2_Y_Var3_Z_data_2.txt              Var1_X_Var2_Y_Var3_Z_data_6.txt
Var1_X_Var2_Y_Var3_Z_data_20.txt             Var1_X_Var2_Y_Var3_Z_data_7.txt
Var1_X_Var2_Y_Var3_Z_data_21.txt             Var1_X_Var2_Y_Var3_Z_data_8.txt
Var1_X_Var2_Y_Var3_Z_data_22.txt             Var1_X_Var2_Y_Var3_Z_data_9.txt

.. that loop would produce

Would rename "Var1_X_Var2_Y_Var3_Z_data_1.txt" into "Var1_X_Var2_Y_Var3_Z_data_01.txt"
Would rename "Var1_X_Var2_Y_Var3_Z_data_2.txt" into "Var1_X_Var2_Y_Var3_Z_data_02.txt"
Would rename "Var1_X_Var2_Y_Var3_Z_data_3.txt" into "Var1_X_Var2_Y_Var3_Z_data_03.txt"
Would rename "Var1_X_Var2_Y_Var3_Z_data_4.txt" into "Var1_X_Var2_Y_Var3_Z_data_04.txt"
Would rename "Var1_X_Var2_Y_Var3_Z_data_5.txt" into "Var1_X_Var2_Y_Var3_Z_data_05.txt"
Would rename "Var1_X_Var2_Y_Var3_Z_data_6.txt" into "Var1_X_Var2_Y_Var3_Z_data_06.txt"
Would rename "Var1_X_Var2_Y_Var3_Z_data_7.txt" into "Var1_X_Var2_Y_Var3_Z_data_07.txt"
Would rename "Var1_X_Var2_Y_Var3_Z_data_8.txt" into "Var1_X_Var2_Y_Var3_Z_data_08.txt"
Would rename "Var1_X_Var2_Y_Var3_Z_data_9.txt" into "Var1_X_Var2_Y_Var3_Z_data_09.txt"

Remove the commented out mv at the end of the loop to actually rename the files.

  • thank you for comments in the code that explain what each part does.
    – Bobby M
    May 21, 2018 at 17:44
find -name "*_[1-9].txt" -exec sh -c 'echo $1 ${1%_*}_0${1##*_}' _ {} \;
  • The $1 is substituting with the file found.
  • The ${1%_*} is removing everything after last underscore and underscore itself.
  • This _0 just prints an underscore followed by a zero.
  • This ${1##*_} removes everything before last underscore and underscore itself.

replace echo with mv for renaming on files.

I used this to crated 3o files

touch Var1_${RANDOM}_Var2_${RANDOM}_Var3_${RANDOM}_data_{1..30}.txt

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