Command to escape a string in bash

Pure Bash, use parameter substitution:

string="Hello\ world"
echo ${string//\\/\\\\} | someprog

In Bash:

printf "%q" "hello\world" | someprog

for example:

printf "%q" "hello\world"
hello\\world

This could be used through variables too:

printf -v var "%q\n" "hello\world"
echo "$var"
hello\\world

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