Check if file exists and whether it contains a specific string - shell

Question

I want to check if file2.sh exists and also if a specific word, poet is part of the file. I use grep to create the variable used_var.
#!/bin/ksh
file_name=/home/file2.sh
used_var=`grep "poet" $file_name`
How can I check if used_var has some value?

Answer 1

Instead of storing the output of grep in a variable and then checking whether the variable is empty, you can do this:
if grep -q "poet" $file_name
then
echo "poet was found in $file_name"
fi
============
Here are some commonly used tests:
-d FILE
FILE exists and is a directory
-e FILE
FILE exists
-f FILE
FILE exists and is a regular file
-h FILE
FILE exists and is a symbolic link (same as -L)
-r FILE
FILE exists and is readable
-s FILE
FILE exists and has a size greater than zero
-w FILE
FILE exists and is writable
-x FILE
FILE exists and is executable
-z STRING
the length of STRING is zero
Example:
if [ -e "$file_name" ] && [ ! -z "$used_var" ]
then
echo "$file_name exists and $used_var is not empty"
fi

Answer 2

if test -e "$file_name";then
...
fi
if grep -q "poet" $file_name; then
..
fi

Answer 3

test -e will test whether a file exists or not. The test command returns a zero value if the test succeeds or 1 otherwise.
Test can be written either as test -e or using []
[ -e "$file_name" ] && grep "poet" $file_name
Unless you actually need the output of grep you can test the return value as grep will return 1 if there are no matches and zero if there are any.
In general terms you can test if a string is non-empty using [ "string" ] which will return 0 if non-empty and 1 if empty

Answer 4

If you have the test binary installed or ksh has a matching built-in function, you could use it to perform your checks. Usually /bin/[ is a symbolic link to test:
if [ -e "$file_name" ]; then
echo "File exists"
fi
if [ -z "$used_var" ]; then
echo "Variable is empty"
fi

Answer 5

You should use the grep -q flag for quiet output. See the man pages below:
man grep output :
General Output Control
-q, --quiet, --silent
Quiet; do not write anything to standard output. Exit immediately with zero status
if any match is found, even if an error was detected. Also see the -s or
--no-messages option. (-q is specified by POSIX.)
This KornShell (ksh) script demos the grep quiet output and is a solution to your question.
grepUtil.ksh :
#!/bin/ksh
#Initialize Variables
file=poet.txt
var=""
dir=tempDir
dirPath="/"${dir}"/"
searchString="poet"
#Function to initialize variables
initialize(){
echo "Entering initialize"
echo "Exiting initialize"
}
#Function to create File with Input
#Params: 1}Directory 2}File 3}String to write to FileName
createFileWithInput(){
echo "Entering createFileWithInput"
orgDirectory=${PWD}
cd ${1}
> ${2}
print ${3} >> ${2}
cd ${orgDirectory}
echo "Exiting createFileWithInput"
}
#Function to create File with Input
#Params: 1}directoryName
createDir(){
echo "Entering createDir"
mkdir -p ${1}
echo "Exiting createDir"
}
#Params: 1}FileName
readLine(){
echo "Entering readLine"
file=${1}
while read line
do
#assign last line to var
var="$line"
done <"$file"
echo "Exiting readLine"
}
#Check if file exists
#Params: 1}File
doesFileExit(){
echo "Entering doesFileExit"
orgDirectory=${PWD}
cd ${PWD}${dirPath}
#echo ${PWD}
if [[ -e "${1}" ]]; then
echo "${1} exists"
else
echo "${1} does not exist"
fi
cd ${orgDirectory}
echo "Exiting doesFileExit"
}
#Check if file contains a string quietly
#Params: 1}Directory Path 2}File 3}String to seach for in File
doesFileContainStringQuiet(){
echo "Entering doesFileContainStringQuiet"
orgDirectory=${PWD}
cd ${PWD}${1}
#echo ${PWD}
grep -q ${3} ${2}
if [ ${?} -eq 0 ];then
echo "${3} found in ${2}"
else
echo "${3} not found in ${2}"
fi
cd ${orgDirectory}
echo "Exiting doesFileContainStringQuiet"
}
#Check if file contains a string with output
#Params: 1}Directory Path 2}File 3}String to seach for in File
doesFileContainString(){
echo "Entering doesFileContainString"
orgDirectory=${PWD}
cd ${PWD}${1}
#echo ${PWD}
grep ${3} ${2}
if [ ${?} -eq 0 ];then
echo "${3} found in ${2}"
else
echo "${3} not found in ${2}"
fi
cd ${orgDirectory}
echo "Exiting doesFileContainString"
}
#-----------
#---Main----
#-----------
echo "Starting: ${PWD}/${0} with Input Parameters: {1: ${1} {2: ${2} {3: ${3}"
#initialize #function call#
createDir ${dir} #function call#
createFileWithInput ${dir} ${file} ${searchString} #function call#
doesFileExit ${file} #function call#
if [ ${?} -eq 0 ];then
doesFileContainStringQuiet ${dirPath} ${file} ${searchString} #function call#
doesFileContainString ${dirPath} ${file} ${searchString} #function call#
fi
echo "Exiting: ${PWD}/${0}"
grepUtil.ksh Output :
user#foo /tmp
$ ksh grepUtil.ksh
Starting: /tmp/grepUtil.ksh with Input Parameters: {1: {2: {3:
Entering createDir
Exiting createDir
Entering createFileWithInput
Exiting createFileWithInput
Entering doesFileExit
poet.txt exists
Exiting doesFileExit
Entering doesFileContainStringQuiet
poet found in poet.txt
Exiting doesFileContainStringQuiet
Entering doesFileContainString
poet
poet found in poet.txt
Exiting doesFileContainString
Exiting: /tmp/grepUtil.ksh