Need a command to remove the last word in the first line of a file

UNIX for Beginners Q & A
1

I have a eg file op.txt

This is a cat
This is a fat cat
This is a fat black cat

I want to remove only the word cat from the first alone .can somebody help.

2 
sed -i '1{s/\w*\W*$//;}' op.txt
3

Try also

awk 'NR == 1 {$NF = ""} 1' file
This is a 
This is a fat cat
This is a fat black cat

awk 'NR == 1 {sub (/cat$/, "")} 1' file
This is a 
This is a fat cat
This is a fat black cat
4 
awk: syntax error near line 1
awk: bailing out near line 1

--- Post updated at 07:02 PM ---

sed: illegal option -- i
error am receiveing
5 
printf "1 s/\\\w*\\\W*$//\nw\nq\n" | ed - op.txt
6

Might have been smart to mention your OS version...

7

Remove the first word in line 2

sed '2 s/^ *[^ ]\{1,\} *//' op.txt

Line 2, s(ubstitute) what the BRE ^ *[^ ]\{1,\} * matches with nothing.
BRE: at the beginning of the line any spaces then at least one non-space then any spaces.

Remove the last word in line 1

sed '1 s/ *[^ ]\{1,\} *$//' op.txt

Line 1, s(ubstitute) what the BRE *[^ ]\{1,\} *$ matches with nothing.
BRE: any spaces then at least one non-space then any spaces at the end of the line.

@rdrtx1, \w and \W and \s and \S are defined in the Perl RE, a newer glibc (GNU-Linux) is needed.

If portability mattters then stick to the original: perl.

perl -i -lpe '$.==1 and s/\s*\S+\s*$//' op.txt

The -i option writes the output back to the input file.

8

Depending of the purpose, if you are in a shell script and need to do this, you might:-

while read line
do
   cut_line="${line% *}"                        # Note that the space is the literal space in the input line
   echo "This is the value of \$cut_line \"${cut_line}\""
done < op.txt

Of course, you could do other things within the loop should you choose.

I hope that this helps,
Robin