| 1 | .TH hush 1 "14 December 2011" "Edgeware tools" |
| 2 | .SH NAME |
| 3 | hush \- run a program, quietly unless it fails |
| 4 | .SH SYNOPSIS |
| 5 | .B hush |
| 6 | .RB [ \-d |
| 7 | .IR directory ] |
| 8 | .RB [ \-m |
| 9 | .IR email-address ] |
| 10 | .RB [ \-n |
| 11 | .IR maxlog ] |
| 12 | .RB [ \-u |
| 13 | .IR owner ][\fB: group ] |
| 14 | .br |
| 15 | \c |
| 16 | .I tag |
| 17 | .I command |
| 18 | .IR arguments ... |
| 19 | .SH DESCRIPTION |
| 20 | The |
| 21 | .B hush |
| 22 | program runs a command. The command's output (i.e., what it writes to |
| 23 | its standard output and standard error file descriptors) is always |
| 24 | logged to a file. If the command succeeds, |
| 25 | .B hush |
| 26 | itself outputs nothing; if it fails, then |
| 27 | .B hush |
| 28 | either writes the command's output to its own stdout, or sends it via |
| 29 | email. It is intended to be used when running noisy programs via |
| 30 | .BR cron (8), |
| 31 | to reduce the amount of uninteresting mail (`cronspam') produced by an |
| 32 | essentially working system. |
| 33 | .PP |
| 34 | The following command-line options are recognized. |
| 35 | .TP |
| 36 | .B \-h |
| 37 | Write a help message describing |
| 38 | .BR hush 's |
| 39 | command line options and usage to standard output, and exit. |
| 40 | .TP |
| 41 | .B \-v |
| 42 | Write |
| 43 | .BR hush 's |
| 44 | version number to standard output, and exit. |
| 45 | .TP |
| 46 | .BI "\-d " directory |
| 47 | Write log files to |
| 48 | .I directory |
| 49 | rather than the default, |
| 50 | .BR "@logdir@" . |
| 51 | .TP |
| 52 | .BI "\-m " email-address |
| 53 | Rather than writing its output to stdout if the command fails, send the |
| 54 | command's output to |
| 55 | .IR email-address . |
| 56 | and exit with status 0. (This is perhaps a surprising choice, but it |
| 57 | prevents the caller from taking additional action to report a problem |
| 58 | which has already been escalated to a human.) |
| 59 | .TP |
| 60 | .BI "\-n " maxlog |
| 61 | If necessary, delete old logfiles so that no more than |
| 62 | .I maxlog |
| 63 | log files are left. |
| 64 | .TP |
| 65 | .BI "\-p " mode |
| 66 | Set the permissions on the logfile to |
| 67 | .I mode , |
| 68 | a mode specification acceptable to |
| 69 | .BR chmod (1), though relative permissions will be applied to mode |
| 70 | .B 600 |
| 71 | (i.e., |
| 72 | .BR u=rw,og= ). |
| 73 | .TP |
| 74 | .BI "\-u \fR[" user\fR][ : group\fR] |
| 75 | Set the ownership and/or group of the logfile. If the |
| 76 | .I user |
| 77 | is specified, then the file's owner is set; if the |
| 78 | .I group |
| 79 | is specified, the file's group is set. (Some care is taken to ensure |
| 80 | that the file is never available to members of the wrong group.) |
| 81 | .SS Operation |
| 82 | The given |
| 83 | .I command |
| 84 | is executed with the |
| 85 | given |
| 86 | .IR arguments , |
| 87 | with stdin redirected from |
| 88 | .BR /dev/null , |
| 89 | and stdout and stderr redirected to separate pipes. If it is available, |
| 90 | .BR stdbuf (1) |
| 91 | is used to ensure that the |
| 92 | .IR command 's |
| 93 | stdout is line-buffered. |
| 94 | .PP |
| 95 | The |
| 96 | .IR command 's |
| 97 | output is collected in a log file named |
| 98 | .IB logdir / tag . date # seq |
| 99 | where |
| 100 | .TP |
| 101 | .I logdir |
| 102 | is the argument of the |
| 103 | .B \-d |
| 104 | option, or |
| 105 | .B @logdir@ |
| 106 | by default; |
| 107 | .TP |
| 108 | .I tag |
| 109 | is the |
| 110 | .I tag |
| 111 | string given to |
| 112 | .B hush |
| 113 | as a command-line argument; |
| 114 | .TP |
| 115 | .I date |
| 116 | is the current date, in ISO8601 form (in local time); and |
| 117 | .TP |
| 118 | .I seq |
| 119 | is a sequence number, chosen to ensure that log file names are distinct |
| 120 | and sort in chronological order. |
| 121 | .PP |
| 122 | The log file begins with a header giving the exact start time (in local |
| 123 | time, with an offset from UTC) and a brief summary of the log format; it |
| 124 | ends with another timestamp and the |
| 125 | .IR command 's |
| 126 | exit status. In between is the command's output. Lines written to |
| 127 | stdout begin with |
| 128 | .RB ` | '; |
| 129 | lines to stderr begin with |
| 130 | .RB ` * '. |
| 131 | The two are interleaved in an attempt to help the reader identify how |
| 132 | much progress the |
| 133 | .I command |
| 134 | had made when it encountered an error; however, because the streams are |
| 135 | read asynchronously, this isn't perfect, and lines may appear earlier or |
| 136 | later than they ought to. |
| 137 | .PP |
| 138 | If the |
| 139 | .I command |
| 140 | succeeds, as mentioned, |
| 141 | .B hush |
| 142 | exits without printing anything. If it fails, and the |
| 143 | .B \-m |
| 144 | option was given, the log file is mailed to the appropriate |
| 145 | .I email-address |
| 146 | with a subject line |
| 147 | .IP |
| 148 | .IB tag : |
| 149 | .I command |
| 150 | .B failed (status = |
| 151 | .IB rc ) |
| 152 | .PP |
| 153 | where |
| 154 | .I rc |
| 155 | is the |
| 156 | .IR command 's |
| 157 | exit status. If no |
| 158 | .B \-m |
| 159 | option was given, this log is simply written to standard output. |
| 160 | .SH BUGS |
| 161 | The stream interleaving isn't quite right, but it's hard to see how to |
| 162 | improve it. |
| 163 | .PP |
| 164 | Capturing the command's output involves making a fairly large number of |
| 165 | auxiliary processes and file descriptors. This is a bit ugly. |
| 166 | .SH AUTHOR |
| 167 | Mark Wooding, <mdw@distorted.org.uk> |
| 168 | .SH SEE ALSO |
| 169 | .BR cron (8). |