filter information by using sed Unix command

I try to filter the system log by running the sed command like:

error
    info_a1
    info_a2
    info_a3
crit
    info_b 
error
   开发者_开发技巧 info_c1 
    info_c2
warn
    info_d 
error
    info_x 
error
    info_p 
info
    info_w 
error
    info_z1 
    info_z2

I expect to get all the error messages like：

error 
    info_a1
    info_a2
    info_a3 
error
    info_c1 
    info_c2
error
    info_x 
error
    info_p
error
    info_z1 
    info_z2

i use

sed -n "/error/, /[info|warn|crit|]/p"

but it does not work pretty well.

---

awk '
  /^error/ {p=1}
  /^(info|warn|crit)/ {p=0}
  p
'

---

If your objective is to print the error message AND the next line after it, then use

cat file_name | grep 'error' -A 1 | grep -v '\-\-'

---

if you just want to get all lines with "error" in it,

grep "error" file

if you insist on sed

sed -n '/error/p' file

or even awk

awk '/error/' file

or Ruby

ruby -ne 'print if /error' file

---

Here is a sed version:

sed -n ':a;/^error/{h;:b;n;${/^[[:blank:]]/{H;x;/^error/{p;q}}};/^[^[:blank:]]/{x;p;x;ba};H;bb}' inputfile

Explanation:

:a                              # label a
/^error/{                       # if pattern space (patt) begins with "error"
    h                           # copy the line to hold space (hold)
    :b                          # label b
        n                       # read the next line
        ${                      # if it's the last line of input
            /^[[:blank:]]/{     # if it begins with a space, tab, etc.
                H               # append it to hold
                x               # exchange patt and hold
                /^error/{       # if patt begins with "error"
                    p           # print it
                    q           # quit
                }
            }
        }
        /^[^[:blank:]]/{        # if patt starts with a non-blank (a new block of input has started
            x                   # exchange patt and hold
            p                   # print patt
            x                   # exchange patt and hold
            ba                  # branch to label a
        }
        H                       # append patt to hold (save a line of the current block)
        bb                      # branch to b
}