Unix'别名'失败了'awk'命令

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, eg: 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 \\n , \\t , ... 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.

Answer 2

You chould use different quotes for surrounding the whole text and for inner strings.

Try changing it to

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

In other words, your outer quotes should be different than the inner ones, so they don't mix.

Answer 3

Community wiki update :

• The redeeming feature of this answer is recognizing that the OP's problem lies in unescaped use of the string delimiters ( ' ) inside a string .
• However, this answer contains general string-handling truths, but does NOT apply to (Bourne-like, POSIX-compatible) shell programming specifically , and thus does not address the OP's problem directly - see the comments.

---

Note: Code snippets are meant to be pseudo code , not shell language.

Basic strings: You canNOT use the same quote within the string as the entire string is delimited with:

foo='hello, 'world!'';
    ^--start string
            ^-- end string
             ^^^^^^^^--- unknown "garbage" causing syntax error.

You have to escape the internal strings:

foo='hello, \'world!\'';
            ^--escape

This is true of pretty much EVERY programming language on the planet. If they don't provide escaping mechanisms, such as \\ , then you have to use alternate means, eg

quotechar=chr(39); // single quote is ascii #39
foo='hello ,' & quotechar & 'world!' & quotechar;

Answer 4

Escape the $ sign not the awk's single quotes and use double quotes for the alias.

Try this :

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