Awk Output

kalyanofb · 02-01-2007, 04:25 AM

--------------------------------------------------------------------------------

i have one file (4geList) which contains two strings(filename) in each line seperated by '|'.

Using the following script:

awk -F '|' '{ printf "%s|%s",system("basename " $1 " .4gl"),system("basename " $2 " .4ge") }' 4geList

It outputs the two string as follows:

menu
main
0|0

My expectation is, it should come
menu|main

Please help me in this problem.

Kalyanaraman

colucix · 02-01-2007, 05:30 AM

What you get is the output of the first basename command, the output of the second one, and finally the exit code of the two commands printed separated by a pipe. The correct way to do this in awk, is:

Code:

gawk -F"|" '{( " basename " $1 )  | getline file1 ; ( " basename " $2 ) | getline file2 ; print file1 "|" file2}' 4geList

Here the construct command | getline var is a way to pass output from a shell command to an awk variable

matthewg42 · 02-01-2007, 05:34 AM

The system function executes an external command and returns the error level. basename happens to print to standard output, so you see the basename of the file in the terminal, but awk gets back only the error level (0 is success), which it puts into the printf placeholders, thus the output you see.

On a broader note, calling external commands should be kept to a minimum because each invocation is expensive. If you're going to have more than a few lines in this file, that's a lot of processes being created, and your program will be slow and un-reliable.

Much better would be to do the basename function internally.

Code:

awk -F'|' 'function bn(p) { n=split(p,a,"/"); return a[n]; }  { printf("%s|%s\n", bn($1), bn($2)); }'

If you are doing this in the middle of a shell script, there's no need even to invoke awk - the shell can do this processing easily enough

Code:

IFS="|"
while read f1 f2; do
        echo "${f1##*/}|${f2##*/}"
done < 4geList

Note that if you want to retain the original IFS value, you can enclose this section in parenthesis - it will then be executed in a sub-shell and prevent modification of the original IFS value.

anomie · 02-01-2007, 10:13 AM

Good thread. Here's another awk way to solve the same problem.

Code:

awk 'BEGIN{ FS="|"; OFS="|"; } 
{ 
sub(/.*\//,"",$1); 
sub(/.*\//,"",$2); 
print $1,$2; 
}' 4geList

For me, this is more straightforward and readable. (Probably because I wrote it.

). Nice to see the other creative / elegant ideas, though.

kalyanofb · 02-02-2007, 02:23 AM

thanks to all of u send the reply.

M. KALYANA RAMAN.