I am trying to write this code so that if the process reads map finished in the pipe it increments a variable by 1 so that it eventually breaks out of the while loop. Otherwise it will add unique parameters to a keys file. However it goes into an infinite loop and never breaks out of the loop.
while [ $a -le 5 ]; do
read input < map_pipe;
if [ $input = "map finished" ]; then
((a++))
echo $a
else
sort -u map_pipe >> keys.txt;
fi
done
I decided to fix it for you, not sure if this is what you wanted, but I think I am close:
#!/bin/bash
a=0 #Initialize your variable to something
while [ $a -le 5 ]; do
read input < map_pipe;
if [ "$input" = "map finished" ]; then #Put double quotes around variables to allow values with spaces
a=$(($a + 1)) #Your syntax was off, use spaces and do something with the output
else
echo $input >> keys.txt #Don't re-read the pipe, it's empty by now and sort will wait for the next input
sort -u keys.txt > tmpfile #Instead sort your file, don't save directly into the same file it will break
mv tmpfile keys.txt
#sort -u keys.txt | sponge keys.txt #Will also work instead of the other sort and mv, but sponge is not installed on most machines
fi
done
Related
I have a following list.txt file with the content
cat list.txt
one
two
zero
three
four
I have a shell script (check.sh) like below,
for i in $(cat list.txt)
do
if [ $i != zero ]; then
echo "the number is $i"
else
exit 1
fi
done
it gives output like below,
./check.sh
the number is one
the number is two
I want to have script which continue with the rest of the items in the list.txt, but it should not process zero and continue with the rest of item.
eg.
the number is one
the number is two
the number is three
the number is four
I tried using "return" but it did not work, gave error.
./check.sh: line 6: return: can only `return' from a function or sourced script
About exit (and return)
The command exit will quit running script. There is no way to continue.
As well, return command will quit function. There in no more way to continue.
About reading input file
For processing line based input file, you'd better to use while read instead of for i in $(cat...:
Simply try:
while read -r i;do
if [ "$i" != "zero" ] ;then
echo number $i
fi
done <list.txt
Alternatively, you could drop unwanted entries before loop:
while read -r i;do
echo number $i
done < <( grep -v ^zero$ <list.txt)
Note: In this specific case, ^zero$ don't need to be quoted. Consider quoting if your string do contain special characters or spaces.
If you have more than one entries to drop, you could use
while read -r i;do echo number $i ;done < <(grep -v '^\(zero\|null\)$' <list.txt)
Alternatively, once input file filtered, use xargs:
If your process is only one single command, you could avoid bash loop by using xargs:
xargs -n 1 echo number < <(grep -v '^\(zero\|null\)$' <list.txt)
How to use continue in bash script
Maybe you are thinking about something like:
while read -r i;do
if [ "$i" = "zero" ] ;then
continue
fi
echo number $i
done <list.txt
Argument of continue is a number representing number of loop to shortcut.
Try this:
for i in {1..5};do
for l in {a..d};do
if [ "$i" -eq 3 ] && [ "$l" = "b" ] ;then
continue 2
fi
echo $i.$l
done
done
(This print 3.a and stop 3 serie at 3.b, breaking 2 loop level)
Then compare with
for i in {1..5};do
for l in {a..d};do
if [ "$i" -eq 3 ] && [ "$l" = "b" ] ;then
continue 1
fi
echo $i.$l
done
done
(This print 3.a , 3.c and 3.d. Only 3.b are skipped, breaking only 1 loop level)
Can anybody tell me what's wrong in this script, it's not working. When I run it, there is no output/error on the screen.
The script is to monitor a log file to check the value of one of the columns, and if it is more than 20 it will echo a message.
#!/bin/bash
while true ; do
COUNT=`tail -f /monitoring/log.20160121|cut -d" " -f39`
echo $COUNT
if [ $COUNT -gt 20 ] ;then
echo "Count is high"
break
fi
sleep 10
done
tail -f does not exit, so your script gets stuck there. I assume you are just interested in the last line of the log; tail -n 1 does that.
Other points:
Indentation: not sure how much got lost while copy pasting, but proper indentation massively increases readability of your code
Variable names: all uppercase variable names are discouraged as they might clash with reserved (environment) variable names
Command substitution with backticks (` `) is discouraged and the form $( ) is preferred; makes for example nesting easier
Since you're using Bash, you can use the (( )) conditional construct, which is better suited for comparing numbers than [ ]
Together:
#!/bin/bash
while true; do
count=$(tail -n 1 /monitoring/log.20160121 | cut -d " " -f 39)
echo $count
if (( count > 20 )); then
echo "Count is high"
break
fi
sleep 10
done
I have stored some arguments value in sample.txt
1 >> sample.txt
2 >> sample.txt
3 >> sample.txt
I have tried to parse the sample.txt in a shell script file to collect and assign the values to specific variables.
#!/bin/sh
if [ -f sample.txt ]; then
cat sample.txt | while read Param
do
let count++
if [ "${count}" == 1 ]; then
Var1=`echo ${Param}`
elif [ "${count}" == 2 ]; then
Var2=`echo ${Param}`
else
Var3=`echo ${Param}`
fi
done
fi
echo "$Var1"
echo "$Var2"
echo results prints nothing. I would expect 1 and 2 should be printed. Anyone help?
You are running the while loop in a subshell; use input redirection instead of cat:
while read Param; do
...
done < sample.txt
(Also, Var1=$Param is much simpler than Var1=$(echo $Param).)
However, there's no point in use a while loop if you know ahead of time how many variables you are setting; just use the right number of read commands directly.
{ read Var1; read Var2; read Var3; } < sample.txt
I'm trying to write a small script that will count entries in a log file, and I'm incrementing a variable (USCOUNTER) which I'm trying to use after the loop is done.
But at that moment USCOUNTER looks to be 0 instead of the actual value. Any idea what I'm doing wrong? Thanks!
FILE=$1
tail -n10 mylog > $FILE
USCOUNTER=0
cat $FILE | while read line; do
country=$(echo "$line" | cut -d' ' -f1)
if [ "US" = "$country" ]; then
USCOUNTER=`expr $USCOUNTER + 1`
echo "US counter $USCOUNTER"
fi
done
echo "final $USCOUNTER"
It outputs:
US counter 1
US counter 2
US counter 3
..
final 0
You are using USCOUNTER in a subshell, that's why the variable is not showing in the main shell.
Instead of cat FILE | while ..., do just a while ... done < $FILE. This way, you avoid the common problem of I set variables in a loop that's in a pipeline. Why do they disappear after the loop terminates? Or, why can't I pipe data to read?:
while read country _; do
if [ "US" = "$country" ]; then
USCOUNTER=$(expr $USCOUNTER + 1)
echo "US counter $USCOUNTER"
fi
done < "$FILE"
Note I also replaced the `` expression with a $().
I also replaced while read line; do country=$(echo "$line" | cut -d' ' -f1) with while read country _. This allows you to say while read var1 var2 ... varN where var1 contains the first word in the line, $var2 and so on, until $varN containing the remaining content.
Always use -r with read.
There is no need to use cut, you can stick with pure bash solutions.
In this case passing read a 2nd var (_) to catch the additional "fields"
Prefer [[ ]] over [ ].
Use arithmetic expressions.
Do not forget to quote variables! Link includes other pitfalls as well
while read -r country _; do
if [[ $country = 'US' ]]; then
((USCOUNTER++))
echo "US counter $USCOUNTER"
fi
done < "$FILE"
minimalist
counter=0
((counter++))
echo $counter
You're getting final 0 because your while loop is being executed in a sub (shell) process and any changes made there are not reflected in the current (parent) shell.
Correct script:
while read -r country _; do
if [ "US" = "$country" ]; then
((USCOUNTER++))
echo "US counter $USCOUNTER"
fi
done < "$FILE"
I had the same $count variable in a while loop getting lost issue.
#fedorqui's answer (and a few others) are accurate answers to the actual question: the sub-shell is indeed the problem.
But it lead me to another issue: I wasn't piping a file content... but the output of a series of pipes & greps...
my erroring sample code:
count=0
cat /etc/hosts | head | while read line; do
((count++))
echo $count $line
done
echo $count
and my fix thanks to the help of this thread and the process substitution:
count=0
while IFS= read -r line; do
((count++))
echo "$count $line"
done < <(cat /etc/hosts | head)
echo "$count"
USCOUNTER=$(grep -c "^US " "$FILE")
Incrementing a variable can be done like that:
_my_counter=$[$_my_counter + 1]
Counting the number of occurrence of a pattern in a column can be done with grep
grep -cE "^([^ ]* ){2}US"
-c count
([^ ]* ) To detect a colonne
{2} the colonne number
US your pattern
Using the following 1 line command for changing many files name in linux using phrase specificity:
find -type f -name '*.jpg' | rename 's/holiday/honeymoon/'
For all files with the extension ".jpg", if they contain the string "holiday", replace it with "honeymoon". For instance, this command would rename the file "ourholiday001.jpg" to "ourhoneymoon001.jpg".
This example also illustrates how to use the find command to send a list of files (-type f) with the extension .jpg (-name '*.jpg') to rename via a pipe (|). rename then reads its file list from standard input.
I am using while loop to read xyz.txt file and file which contains contents like below:
2 - info1
4 - info2
6 - info3
9 - info4
Further I am using if condition to match the count -gt then y value so it will send an email. The problem I am facing every time it matches the if condition it is sending an email which I want once, it should read the file till end and if condition matches store the next line output to a file and then send that file with all information. At present I am receiving number of email.
Hope my question is clear I think I am looking for return function once condition matches it continue reading file till the end and store the info.
count=`echo $line | awk '{print $3}'`
cnt=o
while read line
do
if [ "$count" -gt "$x" ]; then ---> This logic is working fine
cnt=$(( $cnt + 1)) --- > This logic is working fine
echo $line > info.txt -----> In info.txt I want to store info in 1 go which ever matches condition.
export info.txt=$info.txt
${PERL_BIN}/perl $send_mail
fi
done < file.txt
If you only want to send email once, don't put the invocation of Perl which sends mail inside the loop; put it outside the loop (after the end of the loop). Use append (>>) to build the file up piecemeal.
count=`echo $line | awk '{print $3}'`
cnt=0 # 0 not o!
while read line
do
if [ "$count" -gt "$x" ]; then
cnt=$(($cnt + 1))
echo $line >> info.txt
fi
done < file.txt
if [ $cnt -gt 0 ]
then
export info_txt=$info.txt
${PERL_BIN}/perl $send_mail
fi
Okay. I've tried to grasp what you want, I think it is this:
First, before the loop, remove any old info.txt file.
rm info.txt
Then, each time through the loop, append new lines to it like so:
echo $line >> info.txt
Notice the double arrows >>. This means append, instead of overwrite.
Finally, do the email sending after the loop.