I want to split the large file into pieces. Filename and the number records per file after split will be provided as arguments/variables to awk.

EG: FILENAME=A_20 (say it has 100 records), NoOfRecordsPerFile=50 The splitted file names must be


The command I am using is:

awk -vNoOfRecordsPerFile -vFILENAME 'NR%NoOfRecordsPerFile==1{x=FILENAME"-"++i".txt"}{print > x}' $FILENAME

I am getting error :

awk: (FILENAME=A_20 FNR=1) fatal expression for `>' has null string value

Am I doing anything wrong.

The same command is working for the other file.

  • Which awk are you using? -vFILENAME and -vNoOfRecordsPerFile are not valid for mawk or GNU awk. – muru Jul 20 '18 at 7:21
  • try double quotes for x. – msp9011 Jul 20 '18 at 7:23
  • I am using gawk – Sreekesh Darshi Jul 20 '18 at 7:24
  • I tried doing this with the shell script variables as well. but the same issue. Command I used is awk NR%"'$NoOfRecordsPerFile'"==1{x="'$FILENAME'""-"++i".txt"}{print > x} $FILENAME. But still I get the same error. My filename is around 48 characters, this should not be a problem I think. – Sreekesh Darshi Jul 20 '18 at 7:33
  • Your comment and question show different commands. Please edit your post to include the actual command you're running. – muru Jul 20 '18 at 7:43

You're using the FILENAME variable with an empty value (you never give FILENAME a value on the command line), this should produce an error even before your awk script starts running. awk already has a variable called FILENAME that you can use. It's the name of the current input file.

Using -vNoOfRecordsPerFile you say you want to assign a value to an awk variable on the command line, but you never give it a value. This should produce a different error from the one you say you're getting. If you wanted it to take the value of the shell variable with the same name, then use -v NoOfRecordsPerFile="$NoOfRecordsPerFile".

So, the final awk command becomes:

awk -v NoOfRecordsPerFile="$NoOfRecordsPerFile" '
    ((NR-1) % NoOfRecordsPerFile) == 0 { x = FILENAME "-" ++i ".txt" }
                                       { print > x                   }' "$FILENAME"
  • OP says they're using GNU awk, and with gawk, I get an error if I try -v FILENAME without assigning a value: gawk: `FILENAME' argument to `-v' not in `var=value' form – muru Jul 21 '18 at 11:54
  • @muru They are 1) not using gawk, or 2) not getting the error they say they are getting, or 3) not running the code they say they are running. – Kusalananda Jul 21 '18 at 12:21

Your error comes from the NR%NoOfRecordsPerFile==1 condition that is not met before using the variable x, so that variable isn't set.

Instead of awk, you could use split:

split -l 50 -d --additional-suffix='.txt' --numeric-suffixes=1 A_20 'A_20-'

This splits the file A_20 into 2 files of 50 lines called A_20-01.txt and A_20-02.txt.

If you want to use awk, you can try this:

awk -v lineno=50 '((NR-1)%lineno)==0{cnt++;f=FILENAME "-" cnt ".txt"}{print >>f}' A_20

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