I am having a bash script which is something like following,
cat filename | while read line
do
read input;
echo $input;
done
but this is clearly not giving me the right output as when I do read in the while loop it tries to read from the file filename because of the possible I/O redirection.
Any other way of doing the same?
Read from the controlling terminal device:
read input </dev/tty
more info: http://compgroups.net/comp.unix.shell/Fixing-stdin-inside-a-redirected-loop
You can redirect the regular stdin through unit 3 to keep the get it inside the pipeline:
{ cat notify-finished | while read line; do
read -u 3 input
echo "$input"
done; } 3<&0
BTW, if you really are using cat this way, replace it with a redirect and things become even easier:
while read line; do
read -u 3 input
echo "$input"
done 3<&0 <notify-finished
Or, you can swap stdin and unit 3 in that version -- read the file with unit 3, and just leave stdin alone:
while read line <&3; do
# read & use stdin normally inside the loop
read input
echo "$input"
done 3<notify-finished
Try to change the loop like this:
for line in $(cat filename); do
read input
echo $input;
done
Unit test:
for line in $(cat /etc/passwd); do
read input
echo $input;
echo "[$line]"
done
I have found this parameter -u with read.
"-u 1" means "read from stdout"
while read -r newline; do
((i++))
read -u 1 -p "Doing $i""th file, called $newline. Write your answer and press Enter!"
echo "Processing $newline with $REPLY" # united input from two different read commands.
done <<< $(ls)
It looks like you read twice, the read inside the while loop is not needed. Also, you don't need to invoke the cat command:
while read input
do
echo $input
done < filename
echo "Enter the Programs you want to run:"
> ${PROGRAM_LIST}
while read PROGRAM_ENTRY
do
if [ ! -s ${PROGRAM_ENTRY} ]
then
echo ${PROGRAM_ENTRY} >> ${PROGRAM_LIST}
else
break
fi
done
Related
I am a beginner and I am wondering if I can get help with this, please. The code should read one line from a file, display it, meet a condition, and then move on to the next line and repeat for as many lines as are in the file. I have been able to come up with a way to do this but this would be better if it was a loop instead. This is what I have so far
output=$(cat urls.txt | sed -n '1p')
read -p "Store $output y or n ?" deci
if [ $deci == "y" ];
then
sed -n '1p' urls.txt >> saved_domains.txt
fi
output=$(cat urls.txt | sed -n '2p')
read -p "Store $output y or n ?" deci
if [ $deci == "y" ];
then
sed -n '2p' urls.txt >> saved_domains.txt
fi
And this goes on, line by line
#!/bin/bash
while read output
do
read -p "Store $output y or n ?" deci < /dev/tty
if [[ "$deci" == "y" ]]
then
echo "$output" >> saved_domains.txt
fi
done < url.txt
You can read the url.txt file into an "output" variable through a while loop and use this to read the output from the user and append to the saved_domains.txt file accordingly.
One thing to note is the use of the < /dev/tty at the end of the read command for user input. This is not usually needed but as we are already reading from standard input through reading from the file, we need to specifically specify that we are reading from the terminal (/dev/tty)
I am looking for a bash script which reads the file content and it should echo the output as mentioned below:
Input File: file.txt
host1a
host2b
host3c
host4e
I want my output like:
--START--
opt1:host1a
opt2:host2b
opt3:host3c
opt4:host4e
--END--
there is a many possibilities, try this way for example.
#!/bin/bash
opt="1";
while read line;
do
if [ ! -z "$line" ]
then
echo "opt$opt:$line"
opt=$(($opt+1))
fi
done <your_input_file.txt
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
Here is my task: read some data from file line by line. For each line, if it satisfies some condition, then ask user to input something and proceed based on the user's input.
I know how to read content line-by-line from a shell script:
while read line; do
echo $line
done < file.txt
However, what if I want to interact with the user inside the loop body. Conceptually, here is what I want:
while read line; do
echo "Is this what you want: $line [Y]es/[n]o"
# Here is the problem:
# I want to read something from standard input here.
# However, inside the loop body, the standard input is redirected to file.txt
read INPUT
if [[ $INPUT == "Y" ]]; then
echo $line
fi
done < file.txt
Should I use another way to read file? or another way to read stdin?
You can open the file on a file descriptor other than standard input. For example:
while read -u 3 line; do # read from fd 3
read -p "Y or N: " INPUT # read from standard input
if [[ $INPUT == "Y" ]]; then
echo $line
fi
done 3< file.txt # open file on fd 3 for input
I'm trying to parse a csv file I made with Google Spreadsheet. It's very simple for testing purposes, and is basically:
1,2
3,4
5,6
The problem is that the csv doesn't end in a newline character so when I cat the file in BASH, I get
MacBook-Pro:Desktop kkSlider$ cat test.csv
1,2
3,4
5,6MacBook-Pro:Desktop kkSlider$
I just want to read line by line in a BASH script using a while loop that every guide suggests, and my script looks like this:
while IFS=',' read -r last first
do
echo "$last $first"
done < test.csv
The output is:
MacBook-Pro:Desktop kkSlider$ ./test.sh
1 2
3 4
Any ideas on how I could have it read that last line and echo it?
Thanks in advance.
You can force the input to your loop to end with a newline thus:
#!/bin/bash
(cat test.csv ; echo) | while IFS=',' read -r last first
do
echo "$last $first"
done
Unfortunately, this may result in an empty line at the end of your output if the input already has a newline at the end. You can fix that with a little addition:
!/bin/bash
(cat test.csv ; echo) | while IFS=',' read -r last first
do
if [[ $last != "" ]] ; then
echo "$last $first"
fi
done
Another method relies on the fact that the values are being placed into the variables by the read but they're just not being output because of the while statement:
#!/bin/bash
while IFS=',' read -r last first
do
echo "$last $first"
done <test.csv
if [[ $last != "" ]] ; then
echo "$last $first"
fi
That one works without creating another subshell to modify the input to the while statement.
Of course, I'm assuming here that you want to do more inside the loop that just output the values with a space rather than a comma. If that's all you wanted to do, there are other tools better suited than a bash read loop, such as:
tr "," " " <test.csv
cat file |sed -e '${/^$/!s/$/\n/;}'| while IFS=',' read -r last first; do echo "$last $first"; done
If the last (unterminated) line needs to be processed differently from the rest, #paxdiablo's version with the extra if statement is the way to go; but if it's going to be handled like all the others, it's cleaner to process it in the main loop.
You can roll the "if there was an unterminated last line" into the main loop condition like this:
while IFS=',' read -r last first || [ -n "$last" ]
do
echo "$last $first"
done < test.csv