If the last pipe is removed, it seems the value will pass and things will work until the connection is no longer active.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 "$wtf" ]] && echo -e "Connected" || echo -e "Wi-Fi Not Connected!"
...that said -- this is really awful code. Readers, please don't consider places where I'm quoting from the OP as condoning same. :)
Related
Problem
I want to find a simple, single line way to pipe a string depending on a certain condition
Attempt
The above code was my attempt at making a pipe conditional depending on a variable called textfolding.
textfolding="ON"
echo "some text blah balh test foo" if [[ "$textfolding" == "ON" ]]; then | fold -s -w "$fold_width" | sed -e "s|^|\t|g"; fi
This obviously did not work.
Final
How could I achieve this on the same one line?
You can't make the pipe itself conditional, but you can include an if block as an element of the pipeline:
echo "some text blah balh test foo" | if [[ "$textfolding" == "ON" ]]; then fold -s -w "$fold_width" | sed -e "s|^|\t|g"; else cat; fi
Here's a more readable version:
echo "some text blah balh test foo" |
if [[ "$textfolding" == "ON" ]]; then
fold -s -w "$fold_width" | sed -e "s|^|\t|g"
else
cat
fi
Note that since the if block is part of the pipeline, you need to include something like an else cat clause (as I did above) so that whether the if condition is true or not, something will pass the piped data through. Without the cat, it'd just get dropped on the metaphorical floor.
How about conditional execution?
textfolding="ON"
string="some text blah balh test foo"
[[ $textfolding == "ON" ]] && echo $string | fold -s -w $fold_width | sed -e "s|^|\t|g" || echo $string
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
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.
I have a text file with host names and IP addresses like so (one IP and one host name per row). The IP addresses and host names can be separated by a spaces and/or a pipe, and the host name may be before or after the IP address
10.10.10.10 HW-DL11_C023
11.11.11.11 HW-DL11_C024
10.10.10.13 | HW-DL12_C023
11.11.11.12 | HW-DL12_C024
HW-DL13_C023 11.10.10.10
HW-DL13_C024 21.11.11.11
HW-DL14_C023 | 11.10.10.10
HW-DL14_C024 | 21.11.11.11
The script below should be able to ping hosts with a common denominator e.g. DL13 (there are two devices and it will ping only those two). What am I doing wrong, as I simply can`t make it work?
The script is in the same directory as the data; I don`t get errors, and everything is formatted. The server is Linux.
pingme () {
hostfile="/home/rex/u128789/hostfile.txt"
IFS= mapfile -t hosts < <(cat $hostfile)
for host in "${hosts[#]}"; do
match=$(echo "$host" | grep -o "\-$1_" | sed 's/-//' | sed 's/_//')
if [[ "$match" = "$1" ]]; then
hostname=$(echo "$host" | awk '{print $2}')
ping -c1 -W1 $(echo "$host" | awk '{print $1}') > /dev/null
if [[ $? = 0 ]]; then
echo "$hostname is alive"
elif [[ $? = 1 ]]; then
echo "$hostname is dead"
fi
fi
done
}
Try adding these two lines to your code:
pingme () {
hostfile="/home/rex/u128789/hostfile.txt"
IFS= mapfile -t hosts < <(cat $hostfile)
for host in "${hosts[#]}"; do
echo "Hostname: $host" # <-------- ADD THIS LINE -------
match=$(echo "$host" | grep -o "\-$1_" | sed 's/-//' | sed 's/_//')
echo "...matched with $match" # <-------- ADD THIS LINE -------
if [[ "$match" = "$1" ]]; then
hostname=$(echo "$host" | awk '{print $2}')
ping -c1 -W1 $(echo "$host" | awk '{print $1}') > /dev/null
if [[ $? = 0 ]]; then
echo "$hostname is alive"
elif [[ $? = 1 ]]; then
echo "$hostname is dead"
fi
fi
done
}
Then when you run it, you should see a list of your hosts, at least.
If you don't then you're not reading your file successfully.
If you do, there's a problem in your per-host logic.
Congratulations! You've divided your problem into two smaller problems. Once you know which half has the problem, keep dividing the problem in half until the smallest possible problem is staring you in the face. You'll probably know the solution at that point. If not, add your findings to the question and we'll help out from there.
The original code doesn't handle the pipe separator or the possibly reversed hostname and IP address in the input file. It also makes a lot of unnecessary use of external programs (grep, sed, ...).
Try this:
# Enable extended glob patterns - e.g. +(pattern-list)
shopt -s extglob
function pingme
{
local -r host_denom=$1
local -r hostfile=$HOME/u128789/hostfile.txt
local ipaddr host tmp
# (Add '|' to the usual characters in IFS)
while IFS=$'| \t\n' read -r ipaddr host ; do
# Swap host and IP address if necessary
if [[ $host == +([0-9]).+([0-9]).+([0-9]).+([0-9]) ]] ; then
tmp=$host
host=$ipaddr
ipaddr=$tmp
fi
# Ping the host if its name contains the "denominator"
if [[ $host == *-"$host_denom"_* ]] ; then
if ping -c1 -W1 -- "$ipaddr" >/dev/null ; then
printf '%s is alive\n' "$host"
else
printf '%s is dead\n' "$host"
fi
fi
done < "$hostfile"
return 0
}
pingme DL13
The final line (call the pingme function) is just an example, but it's essential to make the code do something.
REX, you need to be more specific about your what IP's you are trying to get from this example. You also don't ping enough times IMO and your script is case sensitive checking the string (not major). Anyway,
First, check that your input and output is working correctly, in this example I'm just reading and printing, if this doesn't work fix permissions etc :
file="/tmp/hostfile.txt"
while IFS= read -r line ;do
echo $line
done < "${file}"
Next, instead of a function first try to make it work as a script, in this example I manually set "match" to DL13, then I read each line (like before) and (1) match on $match, if found I remove the '|', and then read the line into an array of 2. if the first array item is an a IP (contains periods) set it as the IP the other as hostname, else set the opposite. Then run the ping test.
# BASH4+ Example:
file="/tmp/hostfile.txt"
match="dl13"
while IFS= read -r line ;do
# -- check for matching string (e.g. dl13 --
[[ "${line,,}" =~ "${match,,}" ]] || continue
# -- We found a match, split out host/ip into vars --
line=$(echo ${line//|})
IFS=' ' read -r -a items <<< "$line"
if [[ "${items[0]}" =~ '.' ]] ;then
host="${items[1]}" ; ip="${items[0]}"
else
host="${items[0]}" ; ip="${items[1]}"
fi
# -- Ping test --
ping -q -c3 "${ip}" > /dev/null
if [ $? -eq 0 ] ;then
echo "$host is alive!"
else
echo "$host is toast!"
fi
done < "${file}"
I am checking to see if a process on a remote server has been killed. The code I'm using is:
if [ `ssh -t -t -i id_dsa headless#remoteserver.com "ps -auxwww |grep pipeline| wc -l" | sed -e 's/^[ \t]*//'` -lt 3 ]
then
echo "PIPELINE STOPPED SUCCESSFULLY"
exit 0
else
echo "PIPELINE WAS NOT STOPPED SUCCESSFULLY"
exit 1
fi
However when I execute this I get:
: integer expression expected
PIPELINE WAS NOT STOPPED SUCCESSFULLY
1
The actual value returned is "1" with no whitespace. I checked that by:
vim <(ssh -t -t -i id_dsa headless#remoteserver.com "ps -auxwww |grep pipeline| wc -l" | sed -e 's/^[ \t]*//')
and then ":set list" which showed only the integer and a line feed as the returned value.
I'm at a loss here as to why this is not working.
If the output of the ssh command is truly just an integer preceded by optional tabs, then you shouldn't need the sed command; the shell will strip the leading and/or trailing whitespace as unnecessary before using it as an operand for the -lt operator.
if [ $(ssh -tti id_dsa headless#remoteserver.com "ps -auxwww | grep -c pipeline") -lt 3 ]; then
It is possible that result of the ssh is not the same when you run it manually as when it runs in the shell. You might try saving it in a variable so you can output it before testing it in your script:
result=$( ssh -tti id_dsa headless#remoteserver.com "ps -auxwww | grep -c pipeline" )
if [ $result -lt 3 ];
The return value you get is not entirely a digit. Maybe some shell-metacharacter/linefeed/whatever gets into your way here:
#!/bin/bash
var=$(ssh -t -t -i id_dsa headless#remoteserver.com "ps auxwww |grep -c pipeline")
echo $var
# just to prove my point here
# Remove all digits, and look wether there is a rest -> then its not integer
test -z "$var" -o -n "`echo $var | tr -d '[0-9]'`" && echo not-integer
# get out all the digits to use them for the arithmetic comparison
var2=$(grep -o "[0-9]" <<<"$var")
echo $var2
if [[ $var2 -lt 3 ]]
then
echo "PIPELINE STOPPED SUCCESSFULLY"
exit 0
else
echo "PIPELINE WAS NOT STOPPED SUCCESSFULLY"
exit 1
fi
As user mbratch noticed I was getting a "\r" in the returned value in addition to the expected "\n". So I changed my sed script so that it stripped out the "\r" instead of the whitespace (which chepner pointed out was unnecessary).
sed -e 's/\r*$//'