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Process Substitution

Process substitution is a form of redirection where the input or output of a process (some sequence of commands) appear as a temporary file. This allows us to use the output of a command as a file.

Types of Process Substitution​

There are two types of process substitution:

  1. Process substitution with input: <()
  2. Process substitution with output: >()

Process Substitution with Input​

Process substitution with input is used to pass the output of a command as a file to another command. For example, to pass the output of ls command to grep command:

grep '.log'  <(ls)
Example 
# Check the files in the current directory
❯ ls
exec.log  exec.sh

# Find all files with `.log` extension
❯ grep '.log'  <(ls)
exec.log

Process Substitution with Output​

Process substitution with output is used to pass the output of a command as a file to another command. For example, to pass the output of echo command to a file:


echo "Hello, World" > >(tee output.txt)
Example 
# Execute the example command
❯ echo "Hello, World" > >(tee output.txt)
Hello, World

# Check the files in the current directory
❯ ls
exec.log  exec.sh  output.txt

# Check the content of the output file
❯ cat output.txt
Hello, World
tip

tee command is used to read from standard input and write to standard output and files.