bash mapfile from command output
Jan 12 2021 4:42 AM

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