搜索关键字：

• use awk to read a file in reverse

参考链接：

• http://www.tek-tips.com/viewthread.cfm?qid=965087
• http://stackoverflow.com/questions/742466/how-can-i-reverse-the-order-of-lines-in-a-file
• http://unix.stackexchange.com/questions/9356/how-can-i-print-lines-from-file-backwards-without-using-tac
• http://stackoverflow.com/questions/14258616/using-tac-to-read-a-file-in-reverse
• http://stackoverflow.com/questions/2301789/read-a-file-in-reverse-order-using-python
• =
• http://www.bashoneliners.com/oneliners/oneliner/popular/
• https://github.com/janosgyerik/bashoneliners

参考解答：

$ awk '{a[++n]=$0}END{for(i=n;i>0;--i)print a[i]}' /path/to/input
$ awk '{a[n++]=$0}END{while(n--)print a[n]}' /path/to/input
$ sed '1!G;h;$!d' /path/to/input
$ sed -n '1!G;h;$p' /path/to/input
$ cat /path/to/input | perl -e 'print reverse <>'

# cat /path/to/input | python -c "import sys
> for line in reversed(sys.stdin.readlines()): print line.rstrip()"

注意，上面这个Python版本的无法写在一行上面，否则会报错：

$ cat /path/to/input | python -c "import sys;for line in reversed(sys.stdin.readlines()): print line.rstrip()"
  File "<string>", line 1
    import sys;for line in reversed(sys.stdin.readlines()): print line.rstrip()
                 ^
SyntaxError: invalid syntax

或

$ cat /path/to/input | python -c "import sys\nfor line in reversed(sys.stdin.readlines()): print line.rstrip()"
  File "<string>", line 1
    import sys\nfor line in reversed(sys.stdin.readlines()): print line.rstrip()
                                                                               ^
SyntaxError: unexpected character after line continuation character

搜索关键字：

• python one line for loop error

解释：

• http://stackoverflow.com/questions/2043453/executing-python-multi-line-statements-in-the-one-line-command-line
• http://stackoverflow.com/questions/18602119/python-command-line-argument-semicolon-loop-error

根据Python的语法规则，while和for语句前面是不能有分号的（复合语句都不能全写在一行）：

while, for can’t have semicolon before, they need to be on one line. If you looked at Python grammar:

compound_stmt ::=  if_stmt
                   | while_stmt
                   | for_stmt
                   | try_stmt
                   | with_stmt
                   | funcdef
                   | classdef
                   | decorated
suite         ::=  stmt_list NEWLINE | NEWLINE INDENT statement+ DEDENT
statement     ::=  stmt_list NEWLINE | compound_stmt
stmt_list     ::=  simple_stmt (";" simple_stmt)* [";"]

you will see that the statements that are part of compound_stmt need to be one one line alone. The only statements that can be separated by semicolon are simple_stmt group:

simple_stmt ::=  expression_stmt
                 | assert_stmt
                 | assignment_stmt
                 | augmented_assignment_stmt
                 | pass_stmt
                 | del_stmt
                 | print_stmt
                 | return_stmt
                 | yield_stmt
                 | raise_stmt
                 | break_stmt
                 | continue_stmt
                 | import_stmt
                 | global_stmt
                 | exec_stmt

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