[SOLVED] Is there a method in shell to ignore escape characters?

Issue

In C#, there is a verbatim string so that,

string c = "hello \t world";               // hello     world
string d = @"hello \t world";              // hello \t world

I am new to shell script, is there a similar method in shell?

Because I have many folders with the name like "Apparel & Accessories > Clothing > Activewear", I want to know if there is a easy way to process the escape characters without write so many .

test.sh

director="Apparel & Accessories > Clothing > Activewear"
# any action to escape spaces, &, >   ???
hadoop fs -ls $director

Solution

For definining the specific string in your example, Apparel & Accessories > Clothing > Activewear, either double quotes or single quotes will work; referring to it later is a different story, however:

In the shell (any POSIX-compatible shell), how you refer to a variable is just as important as how you define it.

To safely refer to a previously defined variable without side-effects, enclose it in double quotes, e.g., "$directory".

To define [a variable as] a literal (verbatim) string:

(By contrast, to define a variable with embedded variable references or embedded command substitutions or embedded arithmetic expressions, use double quotes (").)

• If your string contains NO single quotes:

  • Use a single-quoted string, e.g.:

        directory='Apparel & Accessories > Clothing > Activewear'
    

A single-quoted string is not subject to any interpretation by the shell, so it's generally the safest option for defining a literal. Note that the string may span multiple lines; e.g.:

        multiline='line 1
        line 2'

• If your string DOES contain single quotes (e.g., I'm here.) and you want a solution that works in all POSIX-compatible shells:

  • Break the string into multiple (single-quoted) parts and splice in single-quote characters:

Note: Sadly, single-quoted strings cannot contain single quotes, not even with escaping.

        directory='I'\''m here.' 

The string is broken into into single-quoted I, followed by literal ' (escaped as an unquoted string as \'), followed by single-quoted m here.. By virtue of having NO spaces between the parts, the result is a single string containing a literal single quote after I.

Alternative: if you don't mind using a multiline statement, you can use a quoted here document, as described at the bottom.

• If your string DOES contain single quotes (e.g., I'm here.) and you want a solution that works in bash, ksh, and zsh:

  • Use ANSI-C quoting:

        directory=$'I\'m here.' 
    

Note: As you can see, ANSI-C quoting allows for escaping single quotes as \', but note the additional implications: other \<char> sequences are subject to interpretation, too; e.g., \n is interpreted as a newline character - see http://www.gnu.org/software/bash/manual/bash.html#ANSI_002dC-Quoting

---

Tip of the hat to @chepner, who points out that the POSIX-compatible way of directly including a single quote in a string to be used verbatim is to use read -r with a here document using a quoted opening delimiter (the -r option ensures that \ characters in the string are treated as literals).

# *Any* form of quoting, not just single quotes, on the opening EOF will work.
# Note that $HOME will by design NOT be expanded.
# (If you didn't quote the opening EOF, it would.)
read -r directory <<'EOF'
I'm here at $HOME
EOF

• Note that here documents create stdin input (which read reads in this case). Therefore, you cannot use this technique to directly pass the resulting string as an argument.

Answered By - mklement0

Answer Checked By - Gilberto Lyons (WPSolving Admin)