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Full Discussion: ksh behavior change on RHEL5
Top Forums Shell Programming and Scripting ksh behavior change on RHEL5 Post 302416706 by bwhitehd on Tuesday 27th of April 2010 01:39:40 PM
Old 04-27-2010
Question ksh behavior change on RHEL5
I recently patched a RHEL5 host from 5.2 to 5.5. There are some scripts that simply do a ps and grep to check for itself before proceeding. I personally don't like the way the scripts are written and would have done it differently. Before I can proceed with patching the production servers, I need to determine why the behaviour changed with these scripts. I've provided a sample script that reproduces the issue and output from both the patched system and a none patched system. Running the script manually everything works as expected, but these run through cron and give different output.

A small oddity I just noticed too, when type 'cat /etc/redhat' and hitting tab on the patched system you can see below that it put a '\' before the '-', but on the unpatched system it does not.

Crontab:
Code:
* * * * * /app2/stage/aim/aim_ap_etl/test.ksh > /app2/stage/aim/aim_ap_etl/test.out 2>&1

Script:
Code:
#!/bin/ksh

echo $0
SCRIPT=${0##*/}
echo $SCRIPT
echo "IFS=xx${IFS}xx"
echo "PS=$(which ps)"
echo "GREP=$(which grep)"
echo "PGREP=$(which pgrep)"
echo "WC=$(which wc)"
echo "Running processes: "
/bin/ps -ef | /bin/grep -v grep | /bin/grep $SCRIPT
/bin/ps -ef | /bin/grep -v grep | /bin/grep -c $SCRIPT
/bin/ps -ef | /bin/grep -v grep | /bin/grep $SCRIPT | /usr/bin/wc -l
/usr/bin/pgrep $SCRIPT | /usr/bin/wc -l
echo "-----------"

proc1=`ps -ef | /bin/grep -v grep | /bin/grep -c $SCRIPT`
echo "proc1=$proc1"

proc2=$(ps -ef | /bin/grep -v grep | /bin/grep -c $SCRIPT)
echo "proc2=$proc2"

proc3=$(/usr/bin/pgrep $SCRIPT | /usr/bin/wc -l)
echo "proc3=$proc3"

echo "Exiting!"
exit

Non-patched
Code:
> uname -a
Linux xxx 2.6.18-92.el5 #1 SMP Tue Apr 29 13:16:15 EDT 2008 x86_64

> cat /etc/redhat-release
Red Hat Enterprise Linux Server release 5.2 (Tikanga)

> echo ${.sh.version}
Version M 1993-12-28 r

Manual output with ksh:
Code:
> ./test.ksh
./test.ksh
test.ksh
IFS=xx 
xx
PS=/bin/ps
GREP=/bin/grep
PGREP=/usr/bin/pgrep
WC=/usr/bin/wc
Running processes: 
infa      2365 24775  0 12:28 pts/2    00:00:00 /bin/ksh ./test.ksh
1
1
1
-----------
proc1=1
proc2=1
proc3=1
Exiting!

Manual output with bash:
Code:
> ./test.bash
./test.bash
test.bash
IFS=xx 
xx
PS=/bin/ps
GREP=/bin/grep
PGREP=/usr/bin/pgrep
WC=/usr/bin/wc
Running processes: 
infa      2914 24775  0 12:30 pts/2    00:00:00 /bin/bash ./test.bash
1
1
1
-----------
proc1=2
proc2=2
proc3=2
Exiting!

Crontab output with ksh:
Code:
> cat test.out
/app2/stage/aim/aim_ap_etl/test.ksh
test.ksh
IFS=xx 
xx
PS=/bin/ps
GREP=/bin/grep
PGREP=/usr/bin/pgrep
WC=/usr/bin/wc
Running processes: 
infa      3823  3820  0 12:36 ?        00:00:00 /bin/sh -c /app2/stage/aim/aim_ap_etl/test.ksh > /app2/stage/aim/aim_ap_etl/test.out 2>&1
infa      3824  3823  0 12:36 ?        00:00:00 /bin/ksh /app2/stage/aim/aim_ap_etl/test.ksh
2
2
1
-----------
proc1=2
proc2=2
proc3=1
Exiting!

Patched
Code:
> uname -a
Linux xxx 2.6.18-194.el5 #1 SMP Tue Mar 16 21:52:39 EDT 2010 x86_64 x86_64 x86_64 GNU/Linux

> cat /etc/redhat\-release                                                                               
Red Hat Enterprise Linux Server release 5.5 (Tikanga)

> echo ${.sh.version}
Version AJM 93t+ 2010-02-02

Manual output with ksh:
Code:
> ./test.ksh
./test.ksh
test.ksh
IFS=xx 
xx
PS=/bin/ps
GREP=/bin/grep
PGREP=/usr/bin/pgrep
WC=/usr/bin/wc
Running processes: 
infa      3288 11352  0 12:27 pts/3    00:00:00 /bin/ksh ./test.ksh
1
1
1
-----------
proc1=2
proc2=2
proc3=2
Exiting!

Manual output with bash:
Code:
> ./test.bash
./test.bash
test.bash
IFS=xx 
xx
PS=/bin/ps
GREP=/bin/grep
PGREP=/usr/bin/pgrep
WC=/usr/bin/wc
Running processes: 
infa      3702 11352  0 12:28 pts/3    00:00:00 /bin/bash ./test.bash
1
1
1
-----------
proc1=2
proc2=2
proc3=2
Exiting!

Crontab output with ksh:
Code:
> cat test.out
/app2/stage/aim/aim_ap_etl/test.ksh
test.ksh
IFS=xx 
xx
PS=/bin/ps
GREP=/bin/grep
PGREP=/usr/bin/pgrep
WC=/usr/bin/wc
Running processes: 
infa      3962  3961  0 12:32 ?        00:00:00 /bin/sh -c /app2/stage/aim/aim_ap_etl/test.ksh > /app2/stage/aim/aim_ap_etl/test.out 2>&1
infa      3963  3962  0 12:32 ?        00:00:00 /bin/ksh /app2/stage/aim/aim_ap_etl/test.ksh
2
2
1
-----------
proc1=3
proc2=3
proc3=2
Exiting!

 

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