logcat 的用法

logcat [options] [filterspecs]
options include:
-s               Set default filter to silent.
                   Like specifying filterspec '*:s'
-f <filename>    Log to file. Default to stdout
-r [<kbytes>]    Rotate log every kbytes. (16 if unspecified). Requires -f
-n <count>       Sets max number of rotated logs to <count>, default 4
-M <1,0>         Set enable copy(Move) the log to oms_log_path
-v <format>      Sets the log print format, where <format> is one of:

Usage:

                   brief process tag thread raw time threadtime long

-c               clear (flush) the entire log and exit
-d               dump the log and then exit (don't block)
-g               get the size of the log's ring buffer and exit
-b <buffer>      request alternate ring buffer
                   ('main' (default), 'radio', 'events')
-B               output the log in binary

filterspecs are a series of
<tag>[:priority]

where <tag> is a log component tag (or * for all) and priority is:
V     Verbose
D     Debug
I     Info
W     Warn
E     Error
F     Fatal
S     Silent (supress all output)

'*' means '*:d' and <tag> by itself means <tag>:v

If not specified on the commandline, filterspec is set from ANDROID_LOG_TAGS.
If no filterspec is found, filter defaults to '*:I'

If not specified with -v, format is set from ANDROID_PRINTF_LOG
or defaults to "brief"

示例：

1. 看radio log
   logcat -b radio
   
        I/RILC     (    46): 39 0d 0a
        I/RILC     (    46): AT[0]< +ECIND: 1,16,99
        I/RILC     (    46): AT[0]< +ECSQ: 16,99
        I/RILC     (    46): <<<< pCh[0]...
        I/RILC     (    46): 0d 0a 2b 45 43 49 4e 44 3a 20 31 2c 31 37 2c 39 39 0d 0a 0d 0a 2b 45 43 53 51 3a 20 31 37 2c 39
        I/RILC     (    46): 39 0d 0a
        I/RILC     (    46): AT[0]< +ECIND: 1,17,99
        I/RILC     (    46): AT[0]< +ECSQ: 17,99
2. 查看warning以上的log
   logcat *:w
   
        E/SensorManager( 102): smjni------jni data_open
        E/         (    49): b433 6155
        E/         (    49): b433 6157
        E/gralloc ( 102): [unregister] handle 0x2debd0 still lock
        W/BatteryService( 102): get battery health[0] 'Charging'
        W/BatteryService( 102): get battery health='Good'
        W/BatteryService( 102): get battery health[0] 'Charging'
        W/BatteryService( 102): get battery health='Good'
3. 过滤查看dalvikvm的log
   logcat -s dalvikvm 或者 logcat dalvikvm *:s
   
        D/dalvikvm( 257): GC freed 1191 objects / 343344 bytes in 65ms
        D/dalvikvm( 257): GC freed 1191 objects / 343400 bytes in 64ms
        D/dalvikvm( 257): GC freed 1191 objects / 343368 bytes in 65ms
        D/dalvikvm( 257): GC freed 1191 objects / 343416 bytes in 70ms
        D/dalvikvm( 257): GC freed 1191 objects / 343384 bytes in 64ms
   
   备注：logcat的过滤方式有点儿怪异，并不是直接指定要过滤的tag并指定priority就行，必须要设定所有的为silent,在此基础上设置的tag过滤才成功。
        所以，logcat appname:v 是不能成功过滤log的。
4. 过滤多个app
   logcat -s dalvikvm vold
   
        D/vold     (    43): door_sock=10
        D/vold     (    43): fw_sock=7
        D/vold     (    43): uevent_sock=6
        D/dalvikvm( 257): GC freed 1191 objects / 343384 bytes in 76ms
        D/dalvikvm( 257): GC freed 1191 objects / 343368 bytes in 81ms
        D/dalvikvm( 257): GC freed 1191 objects / 343400 bytes in 64ms
        D/vold     (    43): select result=1
5. log保存到文件
   logcat > 1.txt (">"是windows用的数据流导向符号）
   
   尝试用-f选项，结果报错。
   logcat -f 1.txt
   couldn't open output file: Read-only file system