I'm new to bash scripting and I'm asking for a little help !
I've got a little scipt in bash that is not making what I want (but almost) and the behavior of my echo command seems strange to me, look at it :
TST='test'
TEST="${ADDR[3]}"_"$TST"
echo $TEST
#result : _test
echo ${ADDR[3]}
#result : 5
How can you explain these results ? Thanks in advance :)
My ADDR var is defined like this :
#parsing the read line, split on whitespace
IFS=' ' read -ra ADDR <<< "$line"
Here is my complete script :
#!/bin/bash
NUMBER=2
{ read ;
while IFS= read -r line; do
echo "$NUMBER : $line"
IFS=' ' read -ra ADDR <<< "$line"
#If the countdown is set to 0, launch the task ans set it to init value
if [ ${ADDR[0]} == '0' ]; then
#task launching
echo `./${ADDR[1]}.sh ${ADDR[2]} &`
TST='test'
TEST=${ADDR[3]}_$TST
echo $TEST
VAR=$(echo -E "${ADDR[3]}" | tr -d '\n')
#countdown set to init value
sed -i "$NUMBER c $VAR ${ADDR[1]} ${ADDR[2]} ${ADDR[3]}" listing.txt
else
sed -i "$NUMBER c $((ADDR-1)) ${ADDR[1]} ${ADDR[2]} ${ADDR[3]}" listing.txt
fi
((NUMBER++))
done } < listing.txt
Answer: the following is fine,
TEST="${ADDR[3]}"_"$TST"
Although I would recommend.
TEST="${ADDR[3]}_${TST}"
What you need to do is dump ${ADDR[3]} before this statement and confirm that ADDR holds the expected values. You may as well dump the entire array with indexes and confirm all entries
for ((i=0; i<${#ADDR[#]}; i++)); do
printf "ADDR[%3d] %s\n" "$i" "${ADDR[$i]}"
done
This will help isolate the issue. Sorry for the earlier answer. Lesson [sleep 1st: answer 2nd]
Related
I have problem with url formatting in bash script. In below code url request:
text="$(lynx --dump https://address/"${array[${i}]}")"
returns HTTP Error 400. The request URL is invalid. I assume that on
"${array[${i}]}"
is something wrong in url part. But I can't figure out what is right format.
#!/bin/bash
saveIFS="$IFS"
IFS=$'\n'
array=($(<words))
IFS="$saveIFS"
elements=${#array[#]}
for (( i=0;i<$elements;i++))
do
text="$(lynx --dump https://address/"${array[${i}]}")"
echo "$text" >> "outputfilename"
fi
done
I also tried:
text="$(lynx --dump https://address/${array[${i}]})"
Try
#!/bin/bash
IFS=$'\n' read -rd '' -a array <words
elements=${#array[#]}
for (( i=0;i<$elements;i++))
do
text="$(lynx --dump https://address/"${array[${i}]}")"
echo "$text" >> "outputfilename"
done
The array variable wasn't being set with array=($(<words))
You can use read or readarray, but this example is with read
Incidentally, putting IFS=$'\n' before read without a command separator ; sets $IFS only for the read command, removing the need to save and re-set $IFS
You don't need an array at all; the following will work in any POSIX-compatible shell, assuming you have one URL component per line:
while IFS= read -r line; do
text=$(lynx --dump https://address/"$line")
echo "$text"
done < words >> output filename
My two cents...
I prefer use printf -v for this, and this could be build like a filter:
catWeb() {
while IFS= read -r word;do
printf -v url "https://address/%s" "$word"
lynx --dump "$url"
done
}
catWeb <words >outputfilename
I was reading windows file. Lines ended with CR LF. So address contains
\r
character. I can remove it:
array[${i}]=${array[${i}]%$'\r'}
Or I can reformat input file so lines end only with LF.
Main structure of working script reading from CR LF file is
#!/bin/bash
IFS=$'\n' read -rd '' -a array <words
elements=${#array[#]}
for (( i=0;i<$elements;i++))
do
array[${i}]=${array[${i}]%$'\r'}
text="$(lynx --dump https://adrress/"${array[${i}]}")"
if [ ${#text} -gt 1 ]
then
echo "$text" >> "filename"
else
echo "${array[${i}]}" >> "filename2"
fi
done
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.
Let me introduce my loop to you all:
NUM_LINE=0
while read line; do
let NUM_LINE+=1
if [ $NUM_LINE -lt 41 ]; then
echo -e "\t$BLANC|$ORIGINAL $line $BLANC|"
else
echo -e "\n\t$BLANC## "$GRIS"Llista de Nodes sel·leccionats $BLANC############$ORIGINAL\n"
read AUX
NUM_LINE=0
fi
done <$NODES
So that:
$BLANC is \033[1;37m
$GRIS same
$ORIGINAL as well
$NODES is the absolute path of a file containg a lot of lines like:
| 23127 myserver 98.194.263.29 |
The Problem:
The echo inside the else statement it's properly triggered.
But it doesn't happen the same with the read statement
Any suggestion?
The reason that the loop doesn't function properly is because read is reading from stdin in both cases. You need to open an alternate file descriptor to your file and read from the file descriptor.
exec 3<$NODES
NUM_LINE=0
while read -u 3 -r line; do
(( NUM_LINE++ ))
if (( NUM_LINE < 41 )); then
echo -e "\t$BLANC|$ORIGINAL $line $BLANC|"
else
echo -e "\n\t$BLANC## "$GRIS"Llista de Nodes sel·leccionats $BLANC############$ORIGINAL\n"
read AUX
NUM_LINE=0
fi
done
This is my very basic script:
temp=hello
while read line;
do
echo ${line}
done
However, ${line} will itself consist of "value of temp = ${temp}"
I want my script to echo "value of temp is hello". I've tried doing many things, even
echo `echo ${line}`
but each time it always just prints "value of temp is ${temp}"
I hope this question is clear. THanks!
What about this?
temp=hello
while read line; do
echo "Value of temp = `eval echo ${line}`"
done
Then in the console just type:
${temp}
Well, I have solutions with eval, but using eval is mauvais ton, actually.
$> cat 7627845.sh
#!/bin/bash
temp=hello
cat file_with_values.log | while read line;
do
eval echo "${line}"
done
$> cat file_with_values.log
value of temp = ${temp}
$> ./7627845.sh
value of temp = hello
Why does read behave differently with the same input from a pipe and a heredoc:
printf "" | while read line; do echo "line=$line"; done # outputs nothing
while read line; do echo "line=$line"; done <<< "" # outputs 'line='
How can I disable output in the second case?
The here document has an implicit newline (\n) at the end; printf "" outputs nothing whatsoever. I don't know offhand of a way to get rid of the implicit newline.
If you can discard all empty lines...
while read line; do if test -n "$line"; then echo "line=$line"; fi; done <<< ""
How about using $'\c':
man bash | less -p '\\c * suppress trailing newline'
str=""
while read line; do echo "line=$line"; done <<<$'\c'"${str}"
str="abc"
while read line; do echo "line=$line"; done <<<$'\c'"${str}"