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Replace a whole line with "#"

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# 1  
Old 04-27-2013
Replace a whole line with "#"
how can i replace the whole line which start with a specific pattern such as "???", with a desired string such as "#" i.e:

in-file:
Code:
TAB 20120201 21:02:02
MRD 20121301 22:21:01
??? 201 256
SAS 20123010 12:25:41
MMT 20120102 11:01:12
POP 20120306 02:01:01
??? TAV 2021 333

out-file:
Code:
TAB 20120201 21:02:02
MRD 20121301 22:21:01
#
SAS 20123010 12:25:41
MMT 20120102 11:01:12
POP 20120306 02:01:01
#

# 2  
Old 04-27-2013
Code:
$ sed "s/^???.*/#/" input
TAB 20120201 21:02:02
MRD 20121301 22:21:01
#
SAS 20123010 12:25:41
MMT 20120102 11:01:12
POP 20120306 02:01:01
#

This User Gave Thanks to hanson44 For This Post:
saeed.soltani
# 3  
Old 04-28-2013
Thank you very much.
# 4  
Old 04-28-2013
With awk
Code:
awk '/^?\?\?/ {$0="#"} 1'

This User Gave Thanks to Jotne For This Post:
saeed.soltani
# 5  
Old 04-28-2013
Quote:
Originally Posted by Jotne
With awk
Code:
awk '/^?\?\?/ {$0="#"} 1'

Hi Jotne,
I don't see the need for the backslashes? Why not just:
Code:
awk '$1=="???"{$0="#"}1' in-file > out-file
    or
awk '/^???/{$0="#"}1' in-file > out-file

Hi saeed.soltani,
This can also be done directly in a shell using only shell built-ins (without awk or sed):
Code:
while read -r f1 rest
do      if [ "$f1" = "???" ]
        then    echo "#"
        else    printf "%s %s\n" "$f1" "$rest"
        fi
done < in-file > out-file

This will work with any shell that recognizes basic Bourne shell syntax (such as bash and ksh; but not csh and its derivatives).
This User Gave Thanks to Don Cragun For This Post:
saeed.soltani
# 6  
Old 04-28-2013
@don: Since awk uses ERE when using matching, ? has a special meaning and needs to be escaped, except for the first ? since it follows a leading caret sign and is therefore not special..
These 2 Users Gave Thanks to Scrutinizer For This Post:
Don Cragun saeed.soltani
# 7  
Old 04-28-2013
Quote:
Originally Posted by Scrutinizer
@don: Since awk uses ERE when using matching, ? has a special meaning and needs to be escaped, except for the first ? since it follows a leading caret sign and is therefore not special..
Yes, obviously. I obviously didn't get enough sleep before sending that message.

For anyone who hasn't followed this discussion, the awk command:
Code:
/^???/{$0="#"}

matches any line with zero or one ? at the start of the line followed by one ? and changes any matching line to an octothorpe (#).

==============
The above analysis is incorrect. As Scrutinizer points out later, the first question mark above produces undefined results unless it is escaped.

The 1st awk script I suggested and the shell script I suggested in message #5 in this thread were correct, but the 2nd awk script should have been:
Code:
awk '/^\?\?\?/{$0="#"}1' in-file > out-file

Last edited by Don Cragun; 04-28-2013 at 03:35 PM..
This User Gave Thanks to Don Cragun For This Post:
saeed.soltani
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