shell_cmds/date/date.1

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  32 .\"     @(#)date.1      8.3 (Berkeley) 4/28/95
  33 .\" $FreeBSD$
  34 .\"
  35 .Dd May 7, 2015
  36 .Dt DATE 1
  37 .Os
  38 .Sh NAME
  39 .Nm date
  40 .Nd display or set date and time
  41 .Sh SYNOPSIS
  42 .Nm
  43 .Op Fl jRu
  44 .Op Fl r Ar seconds | Ar filename
  45 .Oo
  46 .Fl v
  47 .Sm off
  48 .Op Cm + | -
  49 .Ar val Op Ar ymwdHMS
  50 .Sm on
  51 .Oc
  52 .Ar ...
  53 .Op Cm + Ns Ar output_fmt
  54 .Nm
  55 .Op Fl jnu
  56 .Sm off
  57 .Op Oo Oo Ar mm Oc Ar dd Oc Ar HH
  58 .Ar MM Oo Oo Ar cc Oc Ar yy Oc Op Ar .ss
  59 .Sm on
  60 .Nm
  61 .Op Fl jnRu
  62 .Fl f Ar input_fmt new_date
  63 .Op Cm + Ns Ar output_fmt
  64 .Nm
  65 .Op Fl d Ar dst
  66 .Op Fl t Ar minutes_west
  67 .Sh DESCRIPTION
  68 When invoked without arguments, the
  69 .Nm
  70 utility displays the current date and time.
  71 Otherwise, depending on the options specified,
  72 .Nm
  73 will set the date and time or print it in a user-defined way.
  74 .Pp
  75 The
  76 .Nm
  77 utility displays the date and time read from the kernel clock.
  78 When used to set the date and time,
  79 both the kernel clock and the hardware clock are updated.
  80 .Pp
  81 Only the superuser may set the date,
  82 and if the system securelevel (see
  83 .Xr securelevel 7 )
  84 is greater than 1,
  85 the time may not be changed by more than 1 second.
  86 .Pp
  87 The options are as follows:
  88 .Bl -tag -width Ds
  89 .It Fl d Ar dst
  90 Set the kernel's value for daylight saving time.
  91 If
  92 .Ar dst
  93 is non-zero, future calls
  94 to
  95 .Xr gettimeofday 2
  96 will return a non-zero for
  97 .Fa tz_dsttime .
  98 .It Fl f
  99 Use
 100 .Ar input_fmt
 101 as the format string to parse the
 102 .Ar new_date
 103 provided rather than using the default
 104 .Sm off
 105 .Oo Oo Oo
 106 .Ar mm Oc
 107 .Ar dd Oc
 108 .Ar HH Oc
 109 .Ar MM
 110 .Oo Oo
 111 .Ar cc Oc
 112 .Ar yy Oc Oo
 113 .Ar .ss Oc
 114 .Sm on
 115 format.
 116 Parsing is done using
 117 .Xr strptime 3 .
 118 .It Fl j
 119 Do not try to set the date.
 120 This allows you to use the
 121 .Fl f
 122 flag in addition to the
 123 .Cm +
 124 option to convert one date format to another.
 125 .It Fl n
 126 By default, if the
 127 .Xr timed 8
 128 daemon is running,
 129 .Nm
 130 sets the time on all of the machines in the local group.
 131 The
 132 .Fl n
 133 option suppresses this behavior and causes the time to be set only on the
 134 current machine.
 135 .It Fl R
 136 Use RFC 2822 date and time output format. This is equivalent to use
 137 .Dq Li %a, %d %b %Y \&%T %z
 138 as
 139 .Ar output_fmt
 140 while
 141 .Ev LC_TIME
 142 is set to the
 143 .Dq C
 144 locale .
 145 .It Fl r Ar seconds
 146 Print the date and time represented by
 147 .Ar seconds ,
 148 where
 149 .Ar seconds
 150 is the number of seconds since the Epoch
 151 (00:00:00 UTC, January 1, 1970;
 152 see
 153 .Xr time 3 ) ,
 154 and can be specified in decimal, octal, or hex.
 155 .It Fl r Ar filename
 156 Print the date and time of the last modification of
 157 .Ar filename .
 158 .It Fl t Ar minutes_west
 159 Set the system's value for minutes west of
 160 .Tn GMT .
 161 .Ar minutes_west
 162 specifies the number of minutes returned in
 163 .Fa tz_minuteswest
 164 by future calls to
 165 .Xr gettimeofday 2 .
 166 .It Fl u
 167 Display or set the date in
 168 .Tn UTC
 169 (Coordinated Universal) time.
 170 .It Fl v
 171 Adjust (i.e., take the current date and display the result of the
 172 adjustment; not actually set the date) the second, minute, hour, month
 173 day, week day, month or year according to
 174 .Ar val .
 175 If
 176 .Ar val
 177 is preceded with a plus or minus sign,
 178 the date is adjusted forwards or backwards according to the remaining string,
 179 otherwise the relevant part of the date is set.
 180 The date can be adjusted as many times as required using these flags.
 181 Flags are processed in the order given.
 182 .Pp
 183 When setting values
 184 (rather than adjusting them),
 185 seconds are in the range 0-59, minutes are in the range 0-59, hours are
 186 in the range 0-23, month days are in the range 1-31, week days are in the
 187 range 0-6 (Sun-Sat),
 188 months are in the range 1-12 (Jan-Dec)
 189 and years are in the range 80-38 or 1980-2038.
 190 .Pp
 191 If
 192 .Ar val
 193 is numeric, one of either
 194 .Ar y ,
 195 .Ar m ,
 196 .Ar w ,
 197 .Ar d ,
 198 .Ar H ,
 199 .Ar M
 200 or
 201 .Ar S
 202 must be used to specify which part of the date is to be adjusted.
 203 .Pp
 204 The week day or month may be specified using a name rather than a
 205 number.
 206 If a name is used with the plus
 207 (or minus)
 208 sign, the date will be put forwards
 209 (or backwards)
 210 to the next
 211 (previous)
 212 date that matches the given week day or month.
 213 This will not adjust the date,
 214 if the given week day or month is the same as the current one.
 215 .Pp
 216 When a date is adjusted to a specific value or in units greater than hours,
 217 daylight savings time considerations are ignored.
 218 Adjustments in units of hours or less honor daylight saving time.
 219 So, assuming the current date is March 26, 0:30 and that the DST adjustment
 220 means that the clock goes forward at 01:00 to 02:00, using
 221 .Fl v No +1H
 222 will adjust the date to March 26, 2:30.
 223 Likewise, if the date is October 29, 0:30 and the DST adjustment means that
 224 the clock goes back at 02:00 to 01:00, using
 225 .Fl v No +3H
 226 will be necessary to reach October 29, 2:30.
 227 .Pp
 228 When the date is adjusted to a specific value that does not actually exist
 229 (for example March 26, 1:30 BST 2000 in the Europe/London timezone),
 230 the date will be silently adjusted forwards in units of one hour until it
 231 reaches a valid time.
 232 When the date is adjusted to a specific value that occurs twice
 233 (for example October 29, 1:30 2000),
 234 the resulting timezone will be set so that the date matches the earlier of
 235 the two times.
 236 .Pp
 237 It is not possible to adjust a date to an invalid absolute day, so using
 238 the switches
 239 .Fl v No 31d Fl v No 12m
 240 will simply fail five months of the year.
 241 It is therefore usual to set the month before setting the day; using
 242 .Fl v No 12m Fl v No 31d
 243 always works.
 244 .Pp
 245 Adjusting the date by months is inherently ambiguous because
 246 a month is a unit of variable length depending on the current date.
 247 This kind of date adjustment is applied in the most intuitive way.
 248 First of all,
 249 .Nm
 250 tries to preserve the day of the month.
 251 If it is impossible because the target month is shorter than the present one,
 252 the last day of the target month will be the result.
 253 For example, using
 254 .Fl v No +1m
 255 on May 31 will adjust the date to June 30, while using the same option
 256 on January 30 will result in the date adjusted to the last day of February.
 257 This approach is also believed to make the most sense for shell scripting.
 258 Nevertheless, be aware that going forth and back by the same number of
 259 months may take you to a different date.
 260 .Pp
 261 Refer to the examples below for further details.
 262 .El
 263 .Pp
 264 An operand with a leading plus
 265 .Pq Sq +
 266 sign signals a user-defined format string
 267 which specifies the format in which to display the date and time.
 268 The format string may contain any of the conversion specifications
 269 described in the
 270 .Xr strftime 3
 271 manual page, as well as any arbitrary text.
 272 A newline
 273 .Pq Ql \en
 274 character is always output after the characters specified by
 275 the format string.
 276 The format string for the default display is
 277 .Dq +%+ .
 278 .Pp
 279 If an operand does not have a leading plus sign, it is interpreted as
 280 a value for setting the system's notion of the current date and time.
 281 The canonical representation for setting the date and time is:
 282 .Pp
 283 .Bl -tag -width Ds -compact -offset indent
 284 .It Ar cc
 285 Century
 286 (either 19 or 20)
 287 prepended to the abbreviated year.
 288 .It Ar yy
 289 Year in abbreviated form
 290 (e.g., 89 for 1989, 06 for 2006).
 291 .It Ar mm
 292 Numeric month, a number from 1 to 12.
 293 .It Ar dd
 294 Day, a number from 1 to 31.
 295 .It Ar HH
 296 Hour, a number from 0 to 23.
 297 .It Ar MM
 298 Minutes, a number from 0 to 59.
 299 .It Ar ss
 300 Seconds, a number from 0 to 61
 301 (59 plus a maximum of two leap seconds).
 302 .El
 303 .Pp
 304 Everything but the minutes is optional.
 305 .Pp
 306 Time changes for Daylight Saving Time, standard time, leap seconds,
 307 and leap years are handled automatically.
 308 .Sh ENVIRONMENT
 309 The following environment variables affect the execution of
 310 .Nm :
 311 .Bl -tag -width Ds
 312 .It Ev TZ
 313 The timezone to use when displaying dates.
 314 The normal format is a pathname relative to
 315 .Pa /usr/share/zoneinfo .
 316 For example, the command
 317 .Dq TZ=America/Los_Angeles date
 318 displays the current time in California.
 319 See
 320 .Xr environ 7
 321 for more information.
 322 .El
 323 .Sh FILES
 324 .Bl -tag -width /var/log/messages -compact
 325 .It Pa /var/log/messages
 326 record of the user setting the time
 327 .El
 328 .Sh EXIT STATUS
 329 The
 330 .Nm
 331 utility exits 0 on success, 1 if unable to set the date, and 2
 332 if able to set the local date, but unable to set it globally.
 333 .Sh EXAMPLES
 334 The command:
 335 .Pp
 336 .Dl "date ""+DATE: %Y-%m-%d%nTIME: %H:%M:%S"""
 337 .Pp
 338 will display:
 339 .Bd -literal -offset indent
 340 DATE: 1987-11-21
 341 TIME: 13:36:16
 342 .Ed
 343 .Pp
 344 In the Europe/London timezone, the command:
 345 .Pp
 346 .Dl "date -v1m -v+1y"
 347 .Pp
 348 will display:
 349 .Pp
 350 .Dl "Sun Jan  4 04:15:24 GMT 1998"
 351 .Pp
 352 where it is currently
 353 .Li "Mon Aug  4 04:15:24 BST 1997" .
 354 .Pp
 355 The command:
 356 .Pp
 357 .Dl "date -v1d -v3m -v0y -v-1d"
 358 .Pp
 359 will display the last day of February in the year 2000:
 360 .Pp
 361 .Dl "Tue Feb 29 03:18:00 GMT 2000"
 362 .Pp
 363 So will the command:
 364 .Pp
 365 .Dl "date -v3m -v30d -v0y -v-1m"
 366 .Pp
 367 because there is no such date as the 30th of February.
 368 .Pp
 369 The command:
 370 .Pp
 371 .Dl "date -v1d -v+1m -v-1d -v-fri"
 372 .Pp
 373 will display the last Friday of the month:
 374 .Pp
 375 .Dl "Fri Aug 29 04:31:11 BST 1997"
 376 .Pp
 377 where it is currently
 378 .Li "Mon Aug  4 04:31:11 BST 1997" .
 379 .Pp
 380 The command:
 381 .Pp
 382 .Dl "date 0613162785"
 383 .Pp
 384 sets the date to
 385 .Dq Li "June 13, 1985, 4:27 PM" .
 386 .Pp
 387 .Dl "date ""+%m%d%H%M%Y.%S"""
 388 .Pp
 389 may be used on one machine to print out the date
 390 suitable for setting on another.
 391 .Pp
 392 The command:
 393 .Pp
 394 .Dl "date 1432"
 395 .Pp
 396 sets the time to
 397 .Li "2:32 PM" ,
 398 without modifying the date.
 399 .Pp
 400 Finally the command:
 401 .Pp
 402 .Dl "date -j -f ""%a %b %d %T %Z %Y"" ""`date`"" ""+%s"""
 403 .Pp
 404 can be used to parse the output from
 405 .Nm
 406 and express it in Epoch time.
 407 .Sh DIAGNOSTICS
 408 Occasionally, when
 409 .Xr timed 8
 410 synchronizes the time on many hosts, the setting of a new time value may
 411 require more than a few seconds.
 412 On these occasions,
 413 .Nm
 414 prints:
 415 .Ql Network time being set .
 416 The message
 417 .Ql Communication error with timed
 418 occurs when the communication
 419 between
 420 .Nm
 421 and
 422 .Xr timed 8
 423 fails.
 424 .Sh LEGACY SYNOPSIS
 425 As above, except for the second line, which is:
 426 .Pp
 427 .Nm
 428 .Op Fl jnu
 429 .Sm off
 430 .Op Oo Oo Oo Oo Ar cc Oc Ar yy Oc Ar mm Oc Ar dd Oc Ar HH
 431 .Ar MM Op Ar .ss
 432 .Sm on
 433 .Sh LEGACY DIAGNOSTICS
 434 When invoked in legacy mode, the following exit values are returned:
 435 .Bl -tag -width X -compact
 436 .It 0
 437 The date was written successfully
 438 .It 1
 439 Unable to set the date
 440 .It 2
 441 Able to set the local date, but unable to set it globally
 442 .El
 443 .Pp
 444 For more information about legacy mode, see
 445 .Xr compat 5 .
 446 .Sh SEE ALSO
 447 .Xr locale 1 ,
 448 .Xr gettimeofday 2 ,
 449 .Xr getutxent 3 ,
 450 .Xr strftime 3 ,
 451 .Xr strptime 3 ,
 452 .Xr timed 8
 453 .Rs
 454 .%T "TSP: The Time Synchronization Protocol for UNIX 4.3BSD"
 455 .%A R. Gusella
 456 .%A S. Zatti
 457 .Re
 458 .Sh STANDARDS
 459 The
 460 .Nm
 461 utility is expected to be compatible with
 462 .St -p1003.2 .
 463 The
 464 .Fl d , f , j , n , r , t ,
 465 and
 466 .Fl v
 467 options are all extensions to the standard.
 468 .Sh HISTORY
 469 A
 470 .Nm
 471 command appeared in
 472 .At v1 .