bash: how to pass command line arguments containing special characters

You can either:

1. Escape each single special symbol with a backslash (as in \[abc\]_\[x\|y\]) or
2. Double-quote the entire argument (as in "[abc]_[x|y]").

EDIT: As some have pointed out, double-quoting does not prevent variable expansion nor command substitution. Therefore if your regex contains something that can be interpreted by bash as one of those, use single quotes instead.

Use single quotes. Single quotes ensure that none of the characters are interpreted.

$ printf %s 'spaces  are  not  interpreted away
neither are new lines
nor variable names $TESTING
nor square brackets [TESTING]
nor pipe characters or redirection symbols | > <
nor the semicolon ;
nor backslashes \a \b \c \\
the only thing that does not work is the single quote itself
'

There are two solutions if you need to embed a single quote:

$ printf '%s\n' '[ Don'"'"'t worry, be happy! ]'
[ Don't worry, be happy! ]
$ printf '%s\n' '[ Don'\''t worry, be happy! ]'
[ Don't worry, be happy! ]

Per man bash

There are three quoting mechanisms: the escape character, single quotes, and double quotes.

A non-quoted backslash (\) is the escape character. It preserves the literal value of the next character that follows, with the exception of <newline>. If a \<newline> pair appears, and the backslash is not itself quoted, the \<newline> is treated as a line continuation (that is, it is removed from the input stream and effectively ignored).

Enclosing characters in single quotes preserves the literal value of each character within the quotes. A single quote may not occur between single quotes, even when preceded by a backslash.

Enclosing characters in double quotes preserves the literal value of all characters within the quotes, with the exception of $, `, \, and, when history expansion is enabled, !. The characters $ and ` retain their special meaning within double quotes. The backslash retains its special meaning only when followed by one of the following characters: $, `, ", \, or <newline>. A double quote may be quoted within double quotes by preceding it with a backslash. If enabled, history expansion will be performed unless an ! appearing in double quotes is escaped using a backslash. The backslash preceding the ! is not removed.

The special parameters * and @ have special meaning when in double quotes (see PARAMETERS below).

Words of the form $'string' are treated specially. The word expands to string, with backslash-escaped characters replaced as specified by the ANSI C standard. Backslash escape sequences, if present, are decoded as follows:

       \a     alert (bell)
       \b     backspace
       \e
       \E     an escape character
       \f     form feed
       \n     new line
       \r     carriage return
       \t     horizontal tab
       \v     vertical tab
       \\     backslash
       \'     single quote
       \"     double quote
       \nnn   the eight-bit character whose value is the octal value nnn
              (one to three digits)
       \xHH   the eight-bit character whose value is the hexadecimal value HH
              (one or two hex digits)
       \uHHHH the Unicode (ISO/IEC 10646) character whose value is
              the hexadecimal value HHHH (one to four hex digits)
       \UHHHHHHHH
              the Unicode (ISO/IEC 10646) character whose value is
              the hexadecimal value HHHHHHHH (one to eight hex digits)
       \cx    a control-x character

The expanded result is single-quoted, as if the dollar sign had not been present.

A double-quoted string preceded by a dollar sign ($"string") will cause the string to be translated according to the current locale. If the current locale is C or POSIX, the dollar sign is ignored. If the string is translated and replaced, the replacement is double-quoted.