linux - Unix 'alias' fails with 'awk' command

Question

I'm creating an alias in Unix and have found that the following command fails..

alias logspace='find /apps/ /opt/ -type f -size +100M -exec ls -lh {} ; | awk '{print $5, $9 }''

I get the following :

awk: cmd. line:1: {print
awk: cmd. line:1:       ^ unexpected newline or end of string

Any ideas on why the piped awk command fails...

Thanks, Shaun.

Answer 1

To complement's @Dropout's helpful answer:

tl;dr

The problem is the OP's attempt to use ' inside a '-enclosed (single-quoted) string.

The most robust solution in this case is to replace each interior ' with ''' (sic):

alias logspace='find /apps/ /opt/ -type f -size +100M -exec ls -lh {} ; | 
                awk '''{print $5, $9 }''''

• Bourne-like (POSIX-compatible) shells do not support using ' chars inside single-quoted ('...'-enclosed) strings AT ALL - not even with escaping.
  • (By contrast, you CAN escape " inside a double-quoted string as ", and, as in @Droput's answer, you can directly, embed ' chars. there, but see below for pitfalls.)
• The solution above effectively builds the string from multiple, single-quoted strings into which literal ' chars. - escaped outside the single-quoted strings as ' - are spliced in.
  Another way of putting it, as @Etan Reisinger has done in a comment: ''' means: "close string", "escape single quote", "start new string".
• When defining an alias, you usually want single quotes around its definition so as to delay evaluation of the command until the alias is invoked.

---

Other solutions and their pitfalls:

The following discusses alternative solutions, based on the following alias:

alias foo='echo A '''*''' is born at $(date)'

Note how the * is effectively enclosed in single quotes - using above technique - so as to prevent pathname expansion when the alias is invoked later.

When invoked, this alias prints literal A * star is born, followed by the then-current date and time, e.g.: A * is born at Mon Jun 16 11:33:19 EDT 2014.

---

Use a feature called ANSI C quoting with shells that support it: bash, ksh, zsh

ANSI C-quoted strings, which are enclosed in $'...', DO allow escaping embedded ' chars. as ':

alias foo=$'echo A '*' is born at $(date)'

Pitfalls:

• This feature is not part of POSIX.
• By design, escape sequences such as , , ... are interpreted, too (in fact, that's the purpose of the feature).

---

Use of alternating quoting styles, as in @Dropout's answer:

Pitfall:

'...' and "..." have different semantics, so substituting one for the other can have unintended side-effects:

alias foo="echo A '*' is born at $(date)" # DOES NOT WORK AS INTENDED

While syntactically correct, this will NOT work as intended, because the use of double quotes causes the shell to expand the command substitution $(date) right away, and thus hardwires the date and time at the time of the alias definition into the alias.

As stated: When defining an alias, you usually want single quotes around its definition so as to delay evaluation of the command until the alias is invoked.

---

Finally, a caveat:

The tricky thing in a Bourne-like shell environment is that embedding ' inside a single-quoted string sometimes - falsely - APPEARS to work (instead of generating a syntax error, as in the question), when it instead does something different:

 alias foo='echo a '*' is born at $(date)'  # DOES NOT WORK AS EXPECTED.

This definition is accepted (no syntax error), but won't work as expected - the right-hand side of the definition is effectively parsed as 3 strings - 'echo a ', *, and ' is born at $(date)', which, due to how the shell parses string (merging adjacent strings, quote removal), results in the following, single, literal string: a * is born at $(date). Since the * is unquoted in the resulting alias definition, it will expand to a list of all file/directory names in the current directory (pathname expansion) when the alias is invoked.