Problem with variable substitution in Korn Shell 3

[Amazator]

Hi friends,

Am trying to write a lil script that reverses a text file top-to-bottom. It's:

#!/usr/bin/ksh
                                                                                                                                                                   
i=$(cat $1 | wc -l)
                                                                                                                                                                   
while [[ $i -ge 1 ]]
do
 head -$i $1 | tail -1 >> $2
 i=`expr $i - 1`
done

When I run this script, it just hangs (probably waiting for some more input??).....if I replace

head -$i ...

with

head -`echo $i` ...

it works! Why is this difference? Am I missing something in my understanding of how a command line is parsed and processed by the Shell? Please help me...would be grateful.

Thnx,
Amazator.

 

[columb]

Your script works fine on AIX 5.1 ML 9. What OS are you running on?

Try amending the first line to

#!/usr/bin/ksh -xv

To see what's going on

Columb Healy

 

[PHV]

You may try this:
typeset -i i=$(cat $1 | wc -l)

Hope This Helps, PH.
Want to get great answers to your Tek-Tips questions? Have a look at FAQ219-2884 or FAQ181-2886

 

[feherke]

Hi

The [tt]wc[/tt] command outputs the result left padded with spaces, so [tt]-$i[/tt] has some spaces in the middle, making it to be interpreted as two separate parameters of the [tt]head[/tt] command. When you [tt]echo[/tt]ed it, the spaces disappeared.

By the way, if your above script was for productivity, not just exercise, take a look at the [tt]tac[/tt] command. ( Is GNU utility, possible to exist only on Linuxes. )

Feherke.

http://rootshell.be/~feherke/

 

[vgersh99]

SED 1liners

 # reverse order of lines (emulates "tac")
 # bug/feature in HHsed v1.5 causes blank lines to be deleted
 sed '1!G;h;$!d'               # method 1
 sed -n '1!G;h;$p'             # method 2

vlad
+----------------------------+
| #include<disclaimer.h> |
+----------------------------+

 

[Mike042]

tail -r neatly does the reversing of a text file, though doesn't address your variable substitution question.

I hope that helps.

Mike

 

[PHV]

Another way:
awk '{a[NR]=$0}END{for(i=NR;--iprint a}' $1 > $2

Hope This Helps, PH.
Want to get great answers to your Tek-Tips questions? Have a look at FAQ219-2884 or FAQ181-2886

 

[Amazator]

Thanks, all you wonderful folks who helped me!

As Columb pointed out, I used the switches -xv for /usr/bin/ksh and saw the debug output and it revealed (let's say i is 9):

 + head - 9 | ...

Probably due to not quoting the "-" character.....it was waiting for my interactive input...the moment I did this:

head "-$i" $1 | ...

it worked.

 

[olded]

Beating this horse entirely to death .....

http://www.samag.com/documents/s=9766/sam0506g/0506g.htm

 

[Amazator]

Folks,

Double-quoting -$i didn't help.....guess Feherke was right.

PHV's suggestion worked out:

typeset -i i=$(cat $1 | wc -l)
[/ccode]

Thnks....