Replace every occurence of a character except the last one in every line

regular expressionsed

I want to replace occurrences of "|" EXCEPT the last one in every line of a file with a space using sed only. I want to avoid doing this:

 sed -e "s/[|]/ /1" -e "s/[|]/ /1" -e "s/[|]/ /1" -e "s/[|]/ /1" -e "s/[|]/ /1"  -e "s/[|]/ /1" -e "s/[|]/ /1" mydata.txt

File input:

FLD1     |SFK TK |FLD2   |FLD4 |FLD5 |-          |20200515 |NNNN |406   RCO 301
FLD1     |SFK TK |FLD2   |FLD4 |FLD5 |-          |20200515 |NNNN |0
FLD1     |SFK TK |FLD2   |FLD4 |FLD5 |-          |20200515 |NNNN |0

File output:

FLD1      SFK TK  FLD2    FLD4  FLD5  -           20200515  NNNN |406   RCO 301
FLD1      SFK TK  FLD2    FLD4  FLD5  -           20200515  NNNN |0
FLD1      SFK TK  FLD2    FLD4  FLD5  -           20200515  NNNN |0

Best Answer

sed ':a;/[|].*[|]/s/[|]/ /;ta' file
  • /[|].*[|]/: If line has two pipes,
  • s/[|]/ /: Substitute the first with a space.
  • ta: If a substitution was made, go back to :a.

Output:

$ sed ':a;/[|].*[|]/s/[|]/ /;ta' file
FLD1      SFK TK  FLD2    FLD4  FLD5  -           20200515  NNNN |406   RCO 301
FLD1      SFK TK  FLD2    FLD4  FLD5  -           20200515  NNNN |0
FLD1      SFK TK  FLD2    FLD4  FLD5  -           20200515  NNNN |0

As @steeldriver has remarked, you can use simply | instead of [|] in a basic regular expression (BRE), as is the case above. If you add the -E flag to sed, extended regular expression (ERE) is enabled and then you need to write [|] or \|.

Just for completeness, POSIX sed specification says that "Editing commands other than {...}, a, b, c, i, r, t, w, :, and # can be followed by a semicolon". Then, a compliant alternative to the above is:

sed -e ':a' -e '/[|].*[|]/s/[|]/ /;t a' file
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