I was checking a korn shell script and I stumbled upon this:
if [[ -n `echo "This is an example." | grep -E "example"` ]]; then
# Do something.
fi
Can someone tell me what the -n is doing?
Suggesting to check this article:
[[ -n "string" ]] true if length of string is greater than zero
Similar to
if [[ `echo "This is an example." | grep -Ec "example"` -gt 0 ]]; then
# Do something.
fi
Also better practice for if statements:
if [[ -n $(echo "This is an example." | grep -E "example") ]]; then
# Do something.
fi
Related
I'm reading/editing a bash git integration script
This snippet is supposed to print ${SYMBOL_GIT_PUSH} or ${SYMBOL_GIT_PULL} alongside how many commits i am behind and/or ahead by.
local marks
while IFS= read -r line; do
if [[ $line =~ ^## ]]; then
[[ $line =~ ahead\ ([0-9]+) ]] && marks+=" ${BASH_REMATCH[1]}${SYMBOL_GIT_PUSH}"
[[ $line =~ behind\ ([0-9]+) ]] && marks+=" ${BASH_REMATCH[1]}${SYMBOL_GIT_PULL}"
else
marks="${SYMBOL_GIT_MODIFIED}${marks}"
break
fi
done < <(git status --porcelain --branch 2>/dev/null)
printf '%s' "$marks"
Example:
4↑ 10↓
It is working, but i am trying to understand it.
Why is there some IFS and how does it work with process substitution?
I've heard process isn't defined in sh. Is there a way to do this the /bin/sh way or at least more efficiently?
I was provided with a link that should explain what IFS does.
I switched mixed up things and managed to remove the process substitution:
local marks
git status --porcelain --branch 2>/dev/null |
while IFS= read -r line; do
if [[ $line =~ ^## ]]; then
[[ $line =~ ahead\ ([0-9]+) ]] && marks+=" ${BASH_REMATCH[1]}${SYMBOL_GIT_PUSH}"
[[ $line =~ behind\ ([0-9]+) ]] && marks+=" ${BASH_REMATCH[1]}${SYMBOL_GIT_PULL}"
else
marks="${SYMBOL_GIT_MODIFIED}${marks}"
break
fi
done
printf '%s\n' "$marks"
But now, the value of $marks isn't saved and it prints nothing.
I was provided with another link that explains why.
Will return and update on what i've found.
I used the command grouping workaround and wrapped the loop and the print statement inside curly braces:
Also, i made the /bin/sh version almost functional (the exception - show how much commits i'm ahead or behind, not hard, i'm sure i'll do something with awk or cut).
I took advantage of fact that grep returns non-0 when nothing matches.
git status --porcelain --branch 2>/dev/null | {
SYMBOL_GIT_PUSH='↑'
SYMBOL_GIT_PULL='↓'
while IFS= read -r line
do
if echo "$line" | egrep -q '^##'
then
echo "$line" | egrep -q 'ahead' && marks="$marks $SYMBOL_GIT_PUSH"
echo "$line" | egrep -q 'behind' && marks="$marks $SYMBOL_GIT_PULL"
else
marks="*$marks"
break
fi
done
printf ' %s' "$marks"
}
This was a fun learning experience! Thanks to everyone who helped. When i find the 100% solution i'll update this.
Here's the bashism-less git info function.
__git() {
git_eng="env LANG=C git"
ref="$($git_eng symbolic-ref --short HEAD 2>/dev/null)"
[ -n "$ref" ] && ref="$SYMBOL_GIT_BRANCH$ref" || ref="$($git_eng describe --tags --always 2>/dev/null)"
[ -n "$ref" ] || return;
git status --porcelain --branch 2>/dev/null | {
SYMBOL_GIT_PUSH='↑'
SYMBOL_GIT_PULL='↓'
while IFS= read -r line
do
if echo "$line" | grep -E -q '^##'
then
echo "$line" | grep -E -q 'ahead' &&
marks="$marks $SYMBOL_GIT_PUSH$(echo "$line" | sed 's/.*\[ahead //g' | sed 's/\].*//g')"
echo "$line" | grep -E -q 'behind' &&
marks="$marks $SYMBOL_GIT_PULL$(echo "$line" | sed 's/.*\[behind //g' | sed 's/\].*//g')"
else
marks="$SYMBOL_GIT_MODIFIED$marks"
break
fi
done
printf ' %s%s' "$ref" "$marks"
}
}
sed searches for [ahead and deletes it, as well as everything before it, then it pipes it into another sed which deletes everything past ]. This way only the number remains.
#!/bin/bash
a=2
b=2
COUNTER=0
sam="abcd"
sam1="xyz"
sam2="mno"
for x in ls | grep .rpm
do
`C=rpm -qpR $x | grep -v CompressedFileNames | grep -v PayloadFilesHavePrefix | wc -l`
if [ "sam2"!="$sam1" ]
then
echo "${sam1}"
echo "${sam2}"
if [ $C -eq $a ]
then
COUNTER=$((COUNTER+1))
echo "${x}"
eval sam=$x
#eval sam1=sam | cut -d '-' -f 1
sam1=`echo "${sam}"| cut -d '-' -f 1`
if [ $COUNTER -eq $b ]
then
break
fi
fi
fi
sam2=`echo "${x}"| cut -d '-' -f 1`
done
This is the output I am getting:
xyz
mno
comps-4ES-0.20050107.x86_64.rpm
comps
comps
comps-4ES-0.20050525.x86_64.rpm
My question is: why is the if condition returning true despite sam1 and sam2 being equal? I have checked for non-equality.
Response is the same even if I use
if [ $C -eq $a ] && [ "$sam2" != " $sam1" ]
As Ansgar Wiechers pointed out, you're missing a "$" in front of the sam2 variable. That way, you're comparing the literal string "sam2" with the string value of $sam1 (which initially is set to "xyz"). What you want to do is compare the string values of both variables:
if [ "$sam2" != "$sam1" ]
Regarding $C, you should only include the commands to be evaluated inside backticks, not the evaluation itself. This is called a command substitution - a subshell is created in which the commands are executed, and the backtick expression is substituted by the computed value. The line should look like this:
C=`rpm -qpR $x | grep -v CompressedFileNames | grep -v PayloadFilesHavePrefix | wc -l`
Your for loop also needs a command substitution: for x in ls | grep .rpm makes it look as if you're piping the output of a for command into grep. What you want to do is iterate over the ls | grep part, which you can do with the following command substitution:
for x in `ls | grep .rpm`
Hi Guys Got the solution:
#!/bin/bash
read -p "enter dep number" a
read -p "enter no of rpms" b
COUNTER=0
sam="abcd"
sam1="xyz"
sam2="mno"
for x in `ls | grep .rpm`
do
C=`rpm -qpR $x |grep -v CompressedFileNames | grep -v PayloadFilesHavePrefix | wc -l`
# echo "${C}:c"
if [ $C -eq $a ] && [ "$sam2" != "$sam1" ]
then
COUNTER=$((COUNTER+1))
# echo "${COUNTER}:counter"
# echo "${x}"
eval sam=$x
#eval sam1=sam | cut -d '-' -f 1
sam1=`echo "${sam}"| cut -d '-' -f 1`
if [ $COUNTER -eq $b ]
then
break
fi
fi
sam2=`echo "${x}"| cut -d '-' -f 1`
#echo "${sam2}"
#echo "${sam1}"
done
If the last pipe is removed, it seems the value will pass and things will work until the connection is no longer active. Then the value then goes empty or null with a double quote still there. The sed command can strip that but the pipe won't let the value afterwards be passed. I'm stuck.
iwgetid wlan0 | grep 'ESSID:' | cut -c 18-24 | wtf=$(echo "$1"
[[ -z "$1" ]] && echo -e "Wi-Fi Not Connected!" || echo -e "Connected"
Anything on the right-hand side of a pipeline is run in a subshell, meaning that assignments done there aren't visible anywhere else in your shell.
Also, where you get $1 from is unclear here -- the values from wtf aren't getting into the positional arguments by anything you're doing. Fixing that:
wtf=$(iwgetid wlan0 | grep 'ESSID:' | cut -c 18-24 | sed -e 's/^"//' -e 's/"$//')
[[ -z "$wtf" ]] && echo -e "Wi-Fi Not Connected!" || echo -e "Connected"
[[ ! -z "$wtf" ]] && echo -e "Connected" || echo -e "Wi-Fi Not Connected!"
...that said -- this is really awful code. Readers, please don't consider places where I'm quoting from the OP as condoning same. :)
I have this
if [[ ! $newstring == *['!'##\$%^\&*()_+]* ]]
then
echo Error - Does not contain One Special Character - $newstring
i=$((i+1))
fi
Which checks if the string only has one single character from the bank, i want to check if it has more than one?
What would be the best way?
Either add a second class
if [[ "$newstring" != *['!'##\$%^\&*\(\)_+]*['!'##\$%^\&*\(\)_+]* ]]
or strip anything else out and check length
t="${newstring//[^!##\$%^\&*()_+]}"
if [ ${#t} -lt 2 ]
We can use tr to solve it.
$ string='Hello-World_12#$##*&%)(!####'
$ number=$(( $(tr -d '[[:alnum:]]' <<< "$string"|wc -m) - 1 ))
$ echo "We have $number of special characters"
$ 16
This should be short and faster.
#!/bin/bash
a='!*#%6789';
if [[ `echo $a | sed "s/\(.\)/\1\n/g"|grep -c "[[:punct:]]"` -gt 1 ]]; then echo shenzi; else echo koba; fi
grep can be useful to provide the match
grep -oP "^[^'\!'##\$%^\&*()_+]*['\!'##\$%^\&*()_+][^'\!'##\$%^\&*()_+]+$"
test
$ echo "#asdfasdf234" | grep -oP "^[^'\!'##\$%^\&*()_+]*['\!'##\$%^\&*()_+][^'\!'##\$%^\&*()_+]+$"
will match the string as
#asdfasdf234
$ echo "#asdf#asdf234" | grep -oP "^[^'\!'##\$%^\&*()_+]*['\!'##\$%^\&*()_+][^'\!'##\$%^\&*()_+]+$"
will not match the string
The if construct can be
echo $newstring| grep -oP "^[^'\!'##\$%^\&*()_+]*['\!'##\$%^\&*()_+][^'\!'##\$%^\&*()_+]+$"
if [[ $? -eq 0 ]] > /dev/null
then
echo Error - Does not contain One Special Character - $newstring
i=$((i+1))
fi
Here the regex
^[^'\!'##\$%^\&*()_+]*['\!'##\$%^\&*()_+][^'\!'##\$%^\&*()_+]+$
matches all strings with exact one occurence of the special character
Being relatively new to anything other than bash scripting, I have created a script to
check if a process is running
output PID's to the shell
if not prompt user input and start etc/etc.
I've moved onto positional parameters and can't see where I'm going wrong:
if [ "$1" == "" ]; then
proc_finder
elif [ $1 != "" ];then
case $1 in
-p | --process )
shift
z=$(ps aux |grep $1 |grep -v grep > /dev/null)
if [ ! -z "$z" ]; then
echo "YES"
else
echo "NO"
fi
;;
* )
echo "Usage -p (process)"
esac
fi
This always seems to return yes even when putting in -p test for example. I know im doing something fundamentally wrong, looking at the verbose output the grep -v grep is being done last hence I believe it always returnes an exit state of 0.
Shouldn't that be if [ $? -eq 0 ]?
EDIT 1
You can try this:
z=`ps aux | grep $1 | grep -v grep > /dev/null`
if [ ! -z "$z" ]; then
echo "YES"
else
echo "NO"
fi
If $z is not empty (-z: test for zero-length string) this implies the process was found with the ps command.
EDIT 2
The ps ... grep ... grep is being redirect to /dev/null. That means z will contain nothing. remove the redirection and z should have some output.
z=`ps aux | grep $1 | grep -v grep`
EDIT 3
Alternatively, you can just do this:
ps aux | grep $1 | grep -v grep > /dev/null 2>&1
if [ $? -eq 0 ]; then
echo "YES"
else
echo "NO"
fi
In this case, you are not saving the grep output. That's good if you don't really need it.