Modify file without opening in vi editor

mufy · 03-31-2010, 08:12 AM

Hey,

I have a single line (digits) file in which I need to replace, say, the 6th & 7th digits with some other values. How can I do that without actually opening the file - from the CLI for example?

I'm trying to incorporate this in a script so that I do not have to manually open the file to make the change.

pixellany · 03-31-2010, 08:18 AM

This should be quite straightforward using tools like SED and AWK.

Are you replacing based on position in the line or on some other criteria?

Show a sample of the file before and after the changes.

mufy · 03-31-2010, 08:22 AM

Based on position and the value will be picked from `date +%m` and substituted using a variable.

Before:
20100301201003300000000000

After:
20100301201003310000000000

pixellany · 03-31-2010, 08:35 AM

Ultra-crude solution:

Code:

[mherring@Ath ~]$ a=20100301201003300000000000
[mherring@Ath ~]$ echo $a|sed -r 's/(.{14})../\199/'

Matches the first 16 characacters on the line--replaces 1-14 in kind, and then inserts "99" for #15 and #16.

Same thing, but inserting from a variable:

Code:

[mherring@Ath ~]$ b=99
[mherring@Ath ~]$ echo $a|sed -r "s/(.{14})../\1$b/"
20100301201003990000000000

Note that the SED command string now has to be in double-quotes.

mufy · 03-31-2010, 08:43 AM

This the error I'm getting:

Code:

# a=20100301201003300000000000
# echo $a|sed -r 's/(.{14})../\199/'
sed: Not a recognized flag: r
Usage:  sed [-n] Script [File ...]
        sed [-n] [-e Script] ... [-f Script_file] ... [File ...]

But the above works well on my RHEL4 box.

bret381 · 03-31-2010, 09:30 AM

ok, I am definately not a sed expert. just learning myself, but from what I understand the -r option is a GNU specific option and would not work on AIX. Not sure if eliminating the -r option would work on AIX though Maybe with the -e option??

pixellany · 03-31-2010, 12:11 PM

find the manual for your version of SED. In GNU-BASH, if you don't use the -r flag, then you have to escape the () and maybe the {}.