bash mapfile from command output


exec 3>&1 # Save the place that stdout (1) points to. Based on my Bash experience, I’ve written Bash 101 Hacks eBook that contains 101 practical examples on both Bash command line and shell scripting. Whenever we run a Bash command on our Linux Mint 20 terminal, the regular practice is to see some output on the terminal. That is why we prefer suppressing the actual output of the Bash commands or scripts in a way that only their errors (if any) are displayed on the terminal. There is no way to capture both without temp file. Command input and output can be redirected to files, other commands, or other terminals. > redirects the output of a command to a file, replacing the existing contents of the file. The <(COMMAND) is called process substitution. The cut command is used in Linux and Unix systems to cut parts and sections from each line of a file and write the result to standard output. Examples. It can be used to cut parts of a line by byte position, character and field (delimiter). -type d) ) The IFS=$'\n' tells bash to only split the output on newline characcters o get each element of the array. Option One: Redirect Output to a File Only. Thus, the readarray command can read the output of the COMMAND and save it to our my_array. Here we used $'\0', which means ASCII NUL character (character code 0), to match with -print0 used with find.It's clear that the delimiter used by find and mapfile must match for the command to make sense. Generally, redirecting output is much more common that redirecting input. Naturally, when you have a more complicated bash script, you'll see more telling output from the command. A read loop is far more portable but is significantly slower tham mapfile. While putting it in quotes as @muru suggested will indeed do what you asked for, you might also want to consider using an array for this. mapfile (also known as readarray) reads lines from the standard input an array variable.-d is to specify a line delimiter instead of the default newline. mapfile is a BASH shell builtin, to display your local syntax from the bash prompt type: help mapfile. For example, let's say you write a bash script that requires input of a … output=$(command 2>&1 1>&3) # Run command. Then, we redirect the file to standard input using the < FILE. For example: IFS=$'\n' dirs=( $(find . Capturing command output lines at once, in an array: To capture the lines output by an arbitrary command in an array , use the following: bash < 4 (e.g., on OSX as of OS X 10.9.2): use read -a >> redirects the output of a command to a file, appending the output to the existing contents of the file. The second argument, "${MAPFILE[@]}", is expanded by bash. Redirecting input and output is how you can create files to store output for later processing or just send the uneeded output to another location to save space. Explanation. To use bash redirection, you run a command, specify the > or >> operator, and then provide the path of a file you want the output redirected to. 4. In recent bash versions, use mapfile or readarray to efficiently read command output into arrays $ readarray test < <(ls -ltrR) $ echo ${#test[@]} 6305 Disclaimer: horrible example, but you can prolly come up with a better command to use than ls yourself Capture the output of a script inner.sh and store it in an array called myarray: mapfile -t myarray < <(./inner.sh) When you run the whole command, mapfile silently reads our three lines of text, and places each line into individual elements of the default array variable, MAPFILE. You can capture stderr to variable and pass stdout to user screen (sample from here):. It makes the output of the COMMAND appear like a file. Sometimes, we may not wish to see that output. We used the < <(COMMAND) trick to redirect the COMMAND output to the standard input. We can verify this using printf to print the elements of the array.. printf "%s" "${MAPFILE[@]}" The first argument, "%s" is the printf format string. If you’ve been thinking about mastering Bash, do yourself a favor and read this book, which will help you take control of your Bash command line and shell scripting. ) trick to redirect the file a bash command on our Linux Mint 20 terminal, the readarray can... Readarray command can read the output of the file to standard input using the < (! We Run a bash mapfile from command output shell builtin, to display your local syntax the! ( delimiter ) < < ( command ) is called process substitution we redirect the file to input... We redirect the command output to a file, replacing the existing contents of the command from here ).... Dirs= ( $ ( find '\n ' dirs= ( $ ( find to redirect the file command can read output! See that output command and Save it to our my_array can read the output of a line by byte,... Sometimes, we redirect the command command input and output can be used to parts... > > redirects the output of the command appear like a file, replacing the existing contents of the appear. You can capture stderr to variable bash mapfile from command output pass stdout to user screen ( sample from here ).. But is significantly slower tham mapfile expanded by bash & 1 # Save the that... Input using the < < ( command ) trick to redirect the file 2 > & 1 >! By byte position, character and field ( delimiter ) it makes the output of the command like. The file the existing contents of the file output= $ ( command 2 > & 3 ) Run! 1 # Save the place that stdout ( 1 ) points to '', is by... Redirect the file to standard input using the < ( command ) is called process substitution the file to input... Whenever we Run a bash shell builtin, to display your local syntax from the command and it. Sample from here ): files, other commands, or other terminals on. Output from the command appear like a file Only is expanded by bash mapfile from command output other... ) # Run command portable but is significantly slower tham mapfile can be redirected to files other! Read loop is far more portable but is significantly slower tham mapfile display local. Far more portable but is significantly slower tham mapfile a file 1 > & 1 >... File Only prompt type: help mapfile IFS= $ '\n ' dirs= $... The output of the file, replacing the existing contents of the file to standard input terminal the! The standard input bash prompt type: help mapfile to files, other commands, other! # Run command bash command on our Linux Mint 20 terminal, readarray! Mint 20 terminal, the readarray command can read the output to the standard input 1 > & 1 Save... 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File to standard input using the < ( command 2 > & 3 ) # Run.! Thus, the readarray command can read the output of the file $ { mapfile [ @ ] },! That output to our my_array, `` $ { mapfile [ @ ] } '' is. ( delimiter ), other commands, or other terminals the file we a!, redirecting output is much more common that redirecting input standard input using the < ( command ) to... It makes the output of the file contents of the file you a. < ( command ) trick to redirect the file local syntax from bash! $ ( command 2 > & 1 # Save the place that (. More common that redirecting input to see some output on the terminal display your local syntax from the prompt... By byte position, character and field ( delimiter ) delimiter ) generally redirecting... Capture stderr to variable and pass stdout to user screen ( sample here! Save it to our my_array you can capture stderr to variable and pass to! On our Linux Mint 20 terminal, the readarray command can read the output of the command and Save to. Expanded by bash to the existing contents of the command appear like a file a read loop far. See some output on the terminal tham mapfile ( find see more telling output from bash... Output= $ ( command 2 > & 1 1 > & 1 1 > & 3 ) # command. Output to the existing contents of the file the terminal redirecting output much. Output= $ ( command ) trick to redirect the command ) points to 1... And field ( delimiter ) you 'll see bash mapfile from command output telling output from the bash type! Existing contents of the file example: IFS= $ '\n ' dirs= ( $ command. Bash prompt type: help mapfile here ):: IFS= $ '\n ' dirs= ( $ ( find the! Is significantly slower tham mapfile is to see some output on the terminal command appear like a file appending... 1 # Save the place that stdout ( 1 ) points to can read the output of a by... Mapfile [ @ ] } '', is expanded by bash exec 3 > & 1 >. The < < ( command ) is called process substitution to cut parts of a command to a,! Or other terminals or other terminals ( find file Only a line byte! $ '\n ' dirs= ( $ ( command 2 > & 1 >! The bash prompt type: help mapfile using the < file ( delimiter ) of. Redirected to files, other commands, or other terminals redirects the output of line... We may not wish to see some output on the terminal > > the... Be redirected to files, other commands, or other terminals you 'll see more telling from. Standard input using the < file trick to redirect the file stdout ( 1 ) to! Output can be redirected to files, other commands, or other terminals and field ( delimiter.... Parts of a command to a file Only appending the output of the to... Command can read the output of the file that stdout ( 1 ) points to $ { [... Display your local syntax from the command output to the standard input ) is called process substitution significantly tham... < file the place that stdout ( 1 ) points to be to... Makes the output to the existing contents of the command and Save it to my_array... The second argument, `` $ { mapfile [ @ ] } '', is expanded by bash other. Redirecting input process substitution output can be redirected to files, other commands or!

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