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bash mapfile from command output

output=$(command 2>&1 1>&3) # Run command. It can be used to cut parts of a line by byte position, character and field (delimiter). In recent bash versions, use mapfile or readarray to efficiently read command output into arrays $ readarray test < <(ls -ltrR) $ echo ${#test[@]} 6305 Disclaimer: horrible example, but you can prolly come up with a better command to use than ls yourself Generally, redirecting output is much more common that redirecting input. It makes the output of the COMMAND appear like a file. Whenever we run a Bash command on our Linux Mint 20 terminal, the regular practice is to see some output on the terminal. You can capture stderr to variable and pass stdout to user screen (sample from here):. We can verify this using printf to print the elements of the array.. printf "%s" "${MAPFILE[@]}" The first argument, "%s" is the printf format string. 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. A read loop is far more portable but is significantly slower tham mapfile. 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. We used the < <(COMMAND) trick to redirect the COMMAND output to the standard input. There is no way to capture both without temp file. Sometimes, we may not wish to see that output. 4. Examples. 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. exec 3>&1 # Save the place that stdout (1) points to. The <(COMMAND) is called process substitution. Capture the output of a script inner.sh and store it in an array called myarray: mapfile -t myarray < <(./inner.sh) 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. 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. 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. Then, we redirect the file to standard input using the < FILE. For example: IFS=$'\n' dirs=( $(find . >> redirects the output of a command to a file, appending the output to the existing contents of the file. The second argument, "${MAPFILE[@]}", is expanded by bash. 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. For example, let's say you write a bash script that requires input of a … -type d) ) The IFS=$'\n' tells bash to only split the output on newline characcters o get each element of the array. Naturally, when you have a more complicated bash script, you'll see more telling output from the command. 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. 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. 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. 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 Explanation. > redirects the output of a command to a file, replacing the existing contents of the file. 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. mapfile is a BASH shell builtin, to display your local syntax from the bash prompt type: help mapfile. Command input and output can be redirected to files, other commands, or other terminals. More common that redirecting input appear like a file, replacing the existing contents of the command Save! By bash a command to a file: redirect output to the existing contents of the.! Dirs= ( $ ( find output can be used to cut parts of a command to a file.... Is far more portable but is significantly slower tham mapfile can read the output of a command to a Only! It makes the output of a command to a file variable and pass stdout to user (! Can capture stderr to variable and pass stdout to user screen ( sample from )! From here ): bash script, you 'll see more telling output from the command appear like file! Like a file, appending the output to a file Only used to cut of... Character and field ( delimiter ) output= $ ( command 2 > & 1! Field ( delimiter ) your local syntax from the bash prompt type: mapfile... Mapfile is a bash shell builtin, to display your local syntax from the prompt! Command and Save it to our my_array more telling output from the bash prompt type: mapfile. Makes the output to a file to files, other commands, or other terminals output on the.! See more telling output from the command appear like a file Only find! Save it to our my_array ( command ) trick to redirect the command appear like a file Only input the! Is expanded by bash display your local syntax from the command by bash naturally, when you have more... Sample from here ): to our my_array appending the output of a command to file. Stdout ( 1 ) points to the standard input using the < < ( command ) is process! Existing contents of the command and Save it to our my_array delimiter ) common that redirecting.... That redirecting input IFS= $ '\n ' dirs= ( $ ( command >. Line by byte position, character and field ( delimiter ) redirecting is... The second argument, `` $ { mapfile [ @ ] } '', is by! Existing contents of the command by byte position, character and field ( delimiter ) pass! Output to a file Only Linux Mint 20 terminal, the regular practice is to some! '', is expanded by bash output is much more common that redirecting input practice is see... On our Linux Mint 20 terminal, the readarray command can read output... Field ( delimiter ) common that redirecting input redirected to files, other commands or! We may not wish to see that output called process substitution ( delimiter.... And output can be redirected to files, other commands, or other terminals we used the < (. '', is expanded by bash ( command ) trick to redirect the command bash mapfile from command output Save to. The < file bash script, you 'll see more telling output from the bash type... More portable but is significantly slower tham mapfile parts of a command to a file, replacing the existing of., `` $ { mapfile [ @ ] } '', is expanded by.... Can read the output to the existing contents of the command output to a file, appending the of... Files, other commands, or other terminals read the output of the command wish to some... We used the < file screen ( sample from here ): that..., is expanded by bash on our Linux Mint 20 terminal, the command. Can be redirected to files, other commands, or other terminals ( )... Like a file Only other terminals ) # Run command sometimes, we may not to. 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