MaxPRafferty MaxPRafferty - 26 days ago 6
Linux Question

How can I remove the last character of a file in unix?

Say I have some arbitrary multi-line text file:

sometext
moretext
lastline


How can I remove only the last character (the e, not the newline or null) of the file without making the text file invalid?

Answer

A simpler approach (outputs to stdout, doesn't update the input file):

sed '$ s/.$//' somefile
  • $ is a Sed address that matches the last input line only, thus causing the following function call (s/.$//) to be executed on the last line only.
  • s/.$// replaces the last character on the (in this case last) line with an empty string; i.e., effectively removes the last char. (before the newline) on the line.
    . matches any character on the line, and following it with $ anchors the match to the end of the line; note how the use of $ in this regular expression is conceptually related, but technically distinct from the previous use of $ as a Sed address.
  • Example with stdin input (assumes Bash, Ksh, or Zsh):

    $ sed '$ s/.$//' <<< $'line one\nline two'
    line one
    line tw
    

To update the input file too (do not use if the input file is a symlink):

sed -i '$ s/.$//' somefile

Note: On OSX, you'd have to use -i '' instead of just -i.
For an overview of the pitfalls associated with -i, see the bottom half of my answer here.