Shell script: Checking if a particular string exists in a file

[Peter Remirez]

HI,
I would like to check if a particular string exists in a file, and if it doesn't, then insert that string in the file.

I was wondering if anyone could show me how I could perform such checks in a SHELL script?

I tried the following method below but it did not work:

#!/bin/sh
if [grep "pglcls01" syslog.conf|wc -l gt 1];then
echo Here
else
echo "echo "my string here" >> /home/file1
fi

duran% ./sys-1
./sys-1: [grep: command not found
wc: gt: No such file or directory
wc: 1]: No such file or directory
0 total
duran% ls -l syslog*
-rw-r----- 1 premir eng 390 Jun 17 17:38 syslog.conf

Also, how what is the syntax to to check if a value is greater than or equal (>=) in SHELL script?

Could some kindly help me out?

Thanks in advance.

[Sridhar Bhaskarla · Accepted solution]

Hi Peter,

There are syntax errors in your script. I modified it to work.

#!/bin/sh
if [ $(grep "pglcls01" syslog.conf|wc -l) -gt 1 ]
then
echo Here
else
echo "echo "my string here"" >> /home/file1
fi

$(commmand) will evaluate the command. You could also use the back ticks (`grep pglcls01 syslog.conf`).

-Sri

[Leif Halvarsson_2]

Hi,
If you just want to check if a string exist in a file you can use the return code:

If grep >/dev/null 2>&1
then
echo "String exist"
else
echo "String don't exist"
fi

[Donny Jekels]

Is there a spesific area where you want to add the string.

At the end of the file?
In the beginning of the file?
Somewhere in the middle?
In the beginning of the line or at the end of the line?

finding if a string of text exists is easy. placing new text in a flat file is also very straitforward, just let me know the answers to these questions and I'll write you a routine - do you prefer perl or shell scripts?

[Caesar_3]

Hello!

Try the next in csh:

grep -q "String" >& /dev/null

if ($status == 0) then
echo "String exist"
else
echo "String" >>
endif

Caesar

[Fragon]

Hi,just a simple way to check if a string exists in a file:

if grep "String" file >/dev/null 2>&1
then
echo "String exists!"
else
echo "String" >>file
fi

To check if a value is greater than or equal, you can use:
if [ ! $a -lt 10 ]

Good luck!
-ux

[Peter Remirez]

Donny,
I would like to have the string preferably at the beginning of the file.

If possible, would like to have the script to written in SHELL.

Thanks very much.

[Fragon]

Just for text file:

if ...
then
...
else
echo "String" >$$.tmp
cat file >>$$.tmp
cat $$.tmp >file
rm $$.tmp
fi

Good luck!
-ux

[Jean-Louis Phelix]

Hi,

So it could b :

if grep -q "pglcls01" syslog.conf
then
echo Here
else
(
echo "Mystring"
cat /home/file1
) > /tmp/tmp$$
mv /home/file1 /home/file1.prev
mv /tmp/tmp$$ /home/file1
fi

Regards.

[Siddhartha M]

#!/bin/sh
CHK=`cat /etc/syslog.conf | grep pglcls01| wc -l`
if [ $CHK != 0 ]
then
echo "required string exists"
else
echo pglcls01 >> /etc/syslog.conf
fi

[Leif Halvarsson_2]

Hi,

Compleating my previous example. The string is added to the beginning of the file if it not exists.

If ! grep -q "string" 2>/dev/null
then
echo "string" >tmpfile
cat >>tmpfile
mv tmpfile
fi

[Edgar Avila]

why don't you try:

#!/bin/sh
if grep "pglcls01" syslog.conf >> /dev/null; then
echo Here
else
echo "echo \"my string here\"" >> /home/file1
fi

or another way...

#!/bin/sh
y=`grep "pglcls01" syslog.conf|wc -l`

if [ $y -gt 1 ]; then
echo Here
else
echo "echo \"my string here\"" >> /home/file1
fi

Also, how what is the syntax to to check if a value is greater than or equal (>=) in SHELL script?
ans: -ge

[Caesar_3]

Hello!

Return to my option:

grep -q "String" >& /dev/null

if ($status == 0) then
echo "String" > /tmp/temp.$$
cat LOGFILE >> /tmp/temp.$$
mv -f /tmp/temp.$$ LOGFILE
endif

Caesar