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Prefix/Suffix on same file

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# 1  
Old 05-04-2015
Bug Prefix/Suffix on same file
Hi,
I want to add prefix and suffix on line# 205 using SED or AWK and want to change on the same file without creating new file.

This command will be used in the bash script

Am using Bash shell

Regards
Nayaj
# 2  
Old 05-04-2015
sed and awk are stream editors. they can read files, but they don't really write them. some sed's have a -i option for in place editing, but it's somewhat broken and isn't portable.
you can use either and write to a new file, and then if that works, move it over the intended file.

Code:
awk 'NR==205 { print "prefix" $0 "suffix"; };1' file > newfile.$$ && mv newfile.$$ file

or use ed, which is a standard line-oriented file editor
Code:
printf '%s\n' '205s/.*/prefix&suffix/' w | ed -s file
    # or as a here-doc:
ed -s file <<!
205s/.*/prefix&suffix/
w
!

# 3  
Old 05-05-2015
Thanks for the quick reply.

I added below statement in my script and getting error.

Code:
 awk 'NR==$(($last_line_num - 6)) {print "<b>" $0 "</b>"; };1' report_out.txt > new_report && mv new_report report_out.txt

Error line:
Code:
awk NR=='$(($last_line_num - 6)) {print "<b>" $0 "</b>"; };1' report_out.txt

Error:
Code:
 awk: (FILENAME=/mypath/report_out.txt FNR=1) fatal: attempt to access field -6

Last edited by Don Cragun; 05-06-2015 at 03:43 AM.. Reason: Add CODE tags.
# 4  
Old 05-05-2015
you can't pass a shell variable into an awk program like that.

Personally I'd go with the ed. A here-doc does expand shell variables.

Code:
ed -s report_out.txt <<!
$((last_line_num - 6))s#.*#<b>&</b>#
w
!

or in bash as a here-string: ed -s report_out.txt <<< $'$((last_line_num-6))s#.*#<b>&</b>#\nw'

or with printf: printf %s\\n "$((last_line_num-6))s#.*#<b>&</b>#" w | ed -s report_out.txt

or fixing the awk solution:
Code:
awk -v line="$((last_line_num - 6))" 'NR==line {print "<b>" $0 "</b>"; next; };1' report_out.txt > new_report && mv new_report report_out.txt

This User Gave Thanks to neutronscott For This Post:
Nayaj
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