Shell Programming and Scripting

I figured this forum needs some laughs , so I am posting this.

And if the answer is - it depends on bash version - do not reply.



This is from "manual"


while CONTROL-COMMAND; do CONSEQUENT-COMMANDS; done

And here is the REAL code - no ";"

Code:

while [ $i -lt 4 ] do xterm & i=$[$i+1] done

I don't know from which "manual" you got that, but there are more errors then correct words in it. Shame on whoever wrote this drivel. The correct form would be:

Code:

while [ $i -lt 4 ] ; do xterm & ; (( i = i+1 )) ; done

or, in a more readable way:

Code:

while [ $i -lt 4 ] ; do
     xterm &
     (( i = i+1 ))
done

Note that [ is actually a real command: it is a different way to invoke /bin/test. Written in "long form" where the command is more easily recognisable it would be:

Code:

while /bin/test $i -lt 4 ; do
     xterm &
     (( i = i+1 ))
done

The command

Code:

/bin/test $i -lt 4

will return 0 (logical TRUE) if the variable i is lower than 4 and 1 (logically FALSE) otherwise. The while-loop is repeated as long as the control-command (in this case /bin/test) returns 0 and stops if it returns 1. The following will read a complete file:

Code:

while read LINE ; do
     echo "== $LINE =="
done < /some/file

because the read-command returns 0 as long as it can read a line but returns 1 when it hits end-of-file.

I hope this helps.

bakunin

A correction:
most shells don't like & ;. Only & was correct.