Commands using read (340)
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1read -p "Please enter the 4chan url: "|egrep '//i.4cdn.org/[a-z0-9]+/src/([0-9]*).(jpg|png|gif)' - -o|nl -s https:|cut -c7-|uniq|wget -nc -i - --random-wait
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this version only uses shell builtins
1alias ...='while read line; do echo -n "."; done && echo ""' -
Filter out lines of input that contain 72, or fewer, characters. This uses bash only. ${#i} is the number of characters in variable i. Show Sample Output
1while read i; do [ ${#i} -gt 72 ] && echo "$i"; done < /path/to/file -
1echo -n test@example.com | md5sum | (read hash dash ; echo "https://secure.gravatar.com/avatar/${hash}")
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1pgrep 'sleep' | while read pid; do pstree -sa -H$pid $pid ; done
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1git verify-pack -v .git/objects/pack/pack-*.idx | grep blob | sort -k3nr | head | while read s x b x; do git rev-list --all --objects | grep $s | awk '{print "'"$b"'",$0;}'; done
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After you run this script, you can check status for broken symlink with this command: find -L . -type l
1find /PATHNAME -type l | while read nullsymlink ; do wrongpath=$(readlink "$nullsymlink") ; right=$(echo "$wrongpath" | sed s'|OLD_STRING|NEW_STRING|') ; ln -fs "$right" "$nullsymlink" ; done -
Working with lists of IP addresses it is sometimes useful to summarize a count of how many times an IP address appears in the file. This example, summarizeIP, uses another function "verifyIP" previously defined in commandlinefu.com to ensure only valid IP addresses get counted. The summary list is presented in count order starting with highest count. Show Sample Output
1function summaryIP() { < $1 awk '{print $1}' | while read ip ; do verifyIP ${ip} && echo ${ip}; done | awk '{ip_array[$1]++} END { for (ip in ip_array) printf("%5d\t%s\n", ip_array[ip], ip)}' | sort -rn; } -
1o=0; git log --oneline | while read l; do printf "%+9s %s\n" "HEAD~${o}" "$l"; o=$(($o+1)); done | less
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retrieve file names back from touch commands for them Show Sample Output
1touch files.txt; cat reorder_files.sh | while read line; do x=`echo $line | sed 's/touch \([a-z0-9\.]\+.*.pdf\);.*/\1/'`; echo $x >> files.txt ; done; -
Adding course name prefix to lecture pdfs Show Sample Output
1ls *.pdf | while read file; do newfile="CS749__${file}"; mv "${file}" "${newfile}"; done; -
Removing Course name prefix added Show Sample Output
1ls *.pdf | while read file; do newfile="${file##CS749__}"; mv "${file}" "${newfile}"; done; -
Create a bash script to change the modification time for each file in 'files.txt' such that they are in the same order as in 'files.txt' File name for bash script specified by variable, 'scriptName'. It is made an executable once writing into it has been completed. Show Sample Output
1scriptName="reorder_files.sh"; echo -e '#!/bin/sh\n' > "${scriptName}"; cat files.txt | while read file; do echo "touch ${file}; sleep 0.5;" >> "${scriptName}"; done; chmod +x "${scriptName}"; -
apt-get install cpulimit
1ps auxf | grep -v grep | grep -E -i "java|kibana" | awk {'print $2'} | while read pid; do cpulimit -l 25 -b -p $pid > /tmp/cpulimit_$pid ;done -
This snippet allows to process the output of any bash command line by line.
1while read -r line; do echo $line; done < <(YOUR COMMAND HERE); -
I learned a few things reading this command. But I did run into a few issues: 1. On systems that don't use GNU echo (e.g. macOS 10.14.5 Mojave), the e option may not be supported. In this case ANSI escape codes will echoed as text and the terminal will not flash, like this: \e[?5h\e[38;5;1m A L E R T Thu Jun 20 16:31:29 PDT 2019 2. Since the read command strips\ignores leading backslashes, if a user types the backslash character once in the loop, it will not break. Typing backslash twice in a loop will break as expected. 3. The foreground color is set to red (\e[38;5;1m) on every loop. This could be set once before we call while, and then reset once when the loop breaks. 4. Instead of resetting the foreground color when it breaks, the video mode is set back to normal (\e[?5l). This has the effect of leaving the terminal text red until it is manually reset. The alternative I'm proposing here addresses these issues. I tested it on macOS and Arch Linux. Show Sample Output
1printf "\e[38;5;1m"; while true; do printf "\e[?5h A L E R T %s\n" "$(date)"; sleep 0.1; printf "\e[?5l"; read -r -s -n1 -t1 && printf "\e[39m" && break; done -
Tails a log and replaces it line-by-line according to whatever you want to replace. Useful if the file writing to the log can't be modified, so you need to modify its output instead. Show Sample Output
1tail -F logfile|while read l; do sed 's/find/replace/g' <<< $l; done -
1cat playlist.txt | while read line; do youtube-dl --extract-audio --audio-format mp3 -o "%(title)s.%(ext)s" ytsearch:"$line" ;done
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This is useful if you add sid, install some packages, then remove sid and want to work out which packages you installed from sid that should be removed (e.g. before an upgrade to the new stable). Alternatively you can think of this as "find installed packages that can no longer be installed."
1aptitude search -F '%p %v %V %O' '?narrow(?not(?archive("^[^n][^o].*$")),?version(CURRENT))' | while IFS=' ' read -r pkg ver candidate origin; do if [[ $ver == "$candidate" ]] && [[ $origin == '(installed locally)' ]]; then echo "$pkg"; fi; done -
customizable context searches - if you know sed, this is a basis for more complex context control than grep --context offers Show Sample Output
0echo -n search\>\ ; read SEARCH_STRING && sed -n "/$SEARCH_STRING/{n;p;n;p;n;p;q}" [file-to-search] -
0'ls -1 *<pattern>* | while read file; do scp $file user@host:/path/; if [[ $? -eq 0 ]]; then rm $file; fi; done'
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0alias scd='dirs -v; echo -n "select number: "; read newdir; cd -"$newdir"'
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Add @mail.com each line of a list Show Sample Output
0while read line; do echo -e "$line@mail.com"; done < list.txt -
or, for a single directory:
for f in *.c; do mv $f "`basename $f .c`".C; doneShow Sample Output0find . -type f -name \*.c | while read f; do mv $f "`basename $f .c`".C; done -
unsets variables used by the one-liner sets up the IFS bash variable to not be affected by whitespace and disables extra glob expansion uses read to slurp the results of the find command into an array selects an element of the array at random to be passed as an argument to mplayer
0unset files i; set -f; O=$IFS; while IFS= read -r -d $'\0' files[i++]; do :; done < <(find . -name '*.avi' -print0) && IFS=$O; set +f && echo "Running: mplayer \"${files[ $(( $RANDOM % ${#files[@]} )) ]}\"" - ‹ First < 5 6 7 8 9 > Last ›
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